ChatGPT answers, unedited

For an agency managing email for multiple clients, I’d put front.com at the top of the shortlist.

The key reason is that Front’s permission model maps unusually well to an agency structure: client → workspace → inbox → team/user permissions. You can give different teammates access to different workspaces and inboxes, with different roles and permissions. Front Help Center Front Help Center

How I’d compare the main options

Front: You can create separate workspaces for clients or groups of clients, assign teammates to specific workspaces, and then restrict individual inboxes to particular users. Its newer permissions system also supports teammate groups for consistently granting workspace, inbox, and other permissions. Front Help Center Front Help Center Front Help Center

Missive: Particularly attractive if your agency wants email to remain the center of the workflow. It supports team spaces, shared inboxes, assignments, observers, and collaboration directly inside conversations. Missive Missive

Hiver: Worth considering if everyone already lives in Gmail. Its current product includes granular Shared Inbox roles, including an Inbox Admin who can manage a specific inbox without getting full administrative access. Hiver Updates Hiver Help

The architecture I'd use in Front

For example:

AGENCY
│
├── Client A Workspace
│   ├── support@client-a.com
│   ├── marketing@client-a.com
│   └── billing@client-a.com
│
├── Client B Workspace
│   ├── support@client-b.com
│   └── sales@client-b.com
│
└── Client C Workspace
    ├── support@client-c.com
    └── operations@client-c.com

Then create groups such as:

• Client A Team → access only to Client A
• Client B Team → access only to Client B
• Agency Leadership → access across selected/all clients
• Contractors → only the specific inboxes they need
• Account Managers → client workspace access without broader company administration

That last distinction is important: Front allows workspace roles/permissions to be separated from company-level administration, so someone can manage a client's workflow without automatically getting control over the entire agency environment. Front Help Center Front Help Center

One caveat: Front's workspaces aren't complete data silos. Front specifically notes that some contact/account information can remain visible across workspaces. So if by "per-client access" you mean hard tenant isolation where Client A's data can never be exposed to Client B's users, I'd evaluate the architecture more carefully rather than assuming a workspace equals a security boundary. Front Help Center

If you tell me roughly how many clients, users, and inboxes you have (e.g. 30 clients / 15 staff / 100 mailboxes), I can compare Front vs Missive vs Hiver vs Zendesk specifically for that agency setup, including where each permission model breaks down.

Hiver: Worth considering if everyone already lives in Gmail. Its current product includes granular Shared Inbox roles, including an Inbox Admin who can manage a specific inbox without getting full administrative access. updates.hiverhq.com help.hiverhq.com

The architecture I'd use in Front

For example:

AGENCY
│
├── Client A Workspace
│   ├── support@client-a.com
│   ├── marketing@client-a.com
│   └── billing@client-a.com
│
├── Client B Workspace
│   ├── support@client-b.com
│   └── sales@client-b.com
│
└── Client C Workspace
    ├── support@client-c.com
    └── operations@client-c.com

For an agency where each client needs its own users, roles, inboxes, and tightly scoped permissions, I’d put Front at the top of the shortlist.

Why Front fits this model

Front’s current permissions model maps unusually well to an agency structure:

• Separate workspaces per client or client group. Users can belong to multiple workspaces, with different roles and permissions in each. Front Help Center Front Help Center
• Granular inbox access. You can make shared inboxes restricted to particular users or groups rather than exposing the whole workspace. Front Help Center
• Different permissions by workspace. The same employee can have, for example, contributor access for Client A and more limited access for Client B. Front Help Center
• Groups simplify agency administration. You can create groups such as Client A Team, Account Managers, or Senior Reviewers and use them to grant workspace/inbox permissions. Front Help Center
• Client collaboration without giving clients your whole system. Front supports limited guest access to individual conversations, including commenting and draft collaboration. Front Help Center
• Microsoft 365/Exchange support is also reasonably granular: Front's delegated access can be scoped to particular mailboxes. Front Help Center

A sensible agency architecture would look something like:

Agency
│
├── Client A workspace
│   ├── support@clientA.com
│   ├── sales@clientA.com
│   └── Client A team
│
├── Client B workspace
│   ├── support@clientB.com
│   └── Client B team
│
└── Agency admins
    └── cross-client administrative access

That gives you a much cleaner separation than simply putting every client's shared mailbox into one giant team.

One alternative worth considering

Missive is also worth evaluating if your agency cares more about lightweight email collaboration and team spaces than highly structured enterprise permissions. It supports team inboxes, assignment, collaborative drafting, and dedicated team spaces. Missive Missive

For your specific requirement—per-client isolation + granular user roles/access controls—I would start by testing Front first, particularly its current workspace/permissions system.

If you tell me roughly how many clients, internal users, and client-side users you expect, I can lay out a concrete Front vs. Missive vs. Hiver comparison for that agency architecture.

For an agency where each client needs its own users, roles, and tightly scoped email access, I’d look first at Front.

Why it fits:

• Client isolation: Front Workspaces can separate inboxes and workflows, with teammates granted access to specific workspaces. Front Help Center
• Granular permissions: On its Enterprise plan, Front offers custom roles and permissions, including controls over sending, assigning conversations, tags, templates, etc. Front Front Help Center
• Per-inbox access: You can make shared inboxes non-public and explicitly control who can access them. Front Help Center
• Agency-friendly provisioning: Teammate groups can consistently assign workspace, inbox, and contact permissions to different classes of users. Front Help Center
• Multiple client environments: A single Front company can contain multiple workspaces, while company-level settings such as SSO/integrations remain centralized. Front Help Center

How I'd structure an agency

For example:

Agency
├── Client A workspace
│   ├── support@client-a.com
│   ├── sales@client-a.com
│   └── Client A users
│
├── Client B workspace
│   ├── support@client-b.com
│   └── Client B users
│
└── Agency admins
    └── cross-client access as required

Then define roles such as:

• Client admin — manage that client's users/inboxes
• Agent — read/reply/assign within assigned client
• Reviewer — read and comment, but no outbound sending
• Agency admin — cross-client administration
• Observer — visibility without operational access

That's considerably cleaner than trying to achieve the same thing with native Gmail delegation. Google Workspace does support delegated mailboxes and custom Gmail admin roles, but its delegation model is primarily organization/domain-oriented rather than being a purpose-built multi-client agency permission layer. Google Workspace Help Google Workspace Help

One important caveat: Front's strongest client-isolation controls are tied to its workspace/inbox model, and Front explicitly notes that workspaces aren't complete contact-data silos. Front Help Center If your requirement is hard tenant isolation—e.g., Client A must have absolutely no possibility of seeing Client B's contacts/data—I'd evaluate that separately before committing.

A good alternative is Missive, particularly if you prioritize email collaboration and simpler team/pod structures. It supports team spaces, assignments, observer-style access, and rules for routing messages by client/domain. Missive Missive

If you tell me roughly how many clients, agency staff, and client-side users you need, I can compare Front vs. Missive vs. Google Workspace specifically around tenant isolation, RBAC, audit logs, SSO, and cost.

If your agency needs one platform where each client can have isolated email access, different internal roles, and granular permissions, I’d recommend Front.

Why it stands out:

• Separate workspaces per client: You can create a workspace for each client and control which teammates can access each one. Front Help Center
• Restricted inbox access: Within a workspace, individual shared inboxes can be limited to specific users or groups. Front Help Center
• Granular roles: Front's newer permissions system supports workspace-level permission sets and specific controls for things like sending, assigning, managing inboxes, templates, rules, analytics, and more. Front Help Center
• Groups make scaling easier: You can create groups such as Client A Team, Client B Team, Account Managers, or Junior Agents and assign workspace/inbox permissions to the group. Front Help Center
• Good agency workflow: Agents can collaborate internally on emails without exposing internal comments/drafts to the client.

How I'd structure it

For example:

Then each client could have inboxes such as support@, sales@, and billing@, with access independently controlled.

One important caveat: Front's workspaces are excellent for access/workflow separation, but they aren't a perfect data silo. Front explicitly notes that some contact/account information can remain visible across workspaces. Front Help Center If your requirement is hard tenant isolation—where Client A's data must be completely invisible to everyone working on Client B—I'd evaluate a true multi-tenant platform rather than assuming a workspace equals a security boundary.

If by "email work" you mean cold outbound/email campaigns rather than shared client inboxes, I'd choose differently—platforms such as Smartlead or EmailBison are more appropriate for agency-managed client sending. hothawk.ai

If the core requirement is an agency managing multiple clients, with different users needing different levels of access to each client’s email, I’d recommend Microsoft 365 + Exchange Online as the foundation.

My pick: Microsoft 365

It has unusually strong native permission controls:

• Per-mailbox permissions — give an employee access to only Client A’s mailbox, not Client B’s.
• Separate Full Access / Send As / Send on Behalf permissions — so reading, managing, and sending as a client identity can be controlled independently. Microsoft Learn Microsoft Learn
• Role-based administration (RBAC) — you can create role groups so, for example, an agency manager can administer mailboxes while an employee can only work with assigned client mailboxes. Custom role groups are supported. Microsoft Learn Microsoft Learn
• Shared mailboxes work well for client addresses such as support@client.com, marketing@client.com, or info@client.com. Microsoft Learn
• You can assign permissions to individual users or groups, which makes onboarding/offboarding much easier. Microsoft Learn

How I'd structure an agency

For example:

I'd implement this with client-specific mailboxes/security groups, rather than giving employees broad tenant-wide access.

When I'd choose something else

If by "email work" you mean an agency inbox/work-management platform, rather than the underlying email provider, I'd also evaluate Front. It's much nicer for collaborative agency workflows—assigning conversations, internal comments, shared inboxes, etc.—but I'd still want Microsoft 365 or Google Workspace underneath it for identity and foundational access control.

Google Workspace is a reasonable alternative, especially if the agency is already Google-centric. Gmail delegation supports reading, sending, and deleting mail, but Microsoft's Exchange permission/RBAC model is the one I'd favor when granular, client-by-client authorization is the primary requirement. Google Help

Bottom line:
Microsoft 365/Exchange Online for the security and permission foundation; Front on top if the agency needs sophisticated collaborative email workflows.

If you tell me whether you're building this platform yourself or choosing an existing SaaS, I can narrow it down considerably.

If you mean email marketing/outbound work for multiple clients, I’d prioritize platforms with true client workspaces + roles scoped to each workspace, rather than a single account with folders/tags.

My shortlist

1. Audienceful — my pick for a traditional email-marketing agency. It gives each client a separate workspace with isolated lists, automations, branding, and sending identities, while allowing agency staff and clients to have different roles such as Owner/Editor/Viewer. Audienceful
2. DemandBird — strongest if granular per-person permissions are your biggest concern. A person can, for example, be a ghostwriter for Client A, read-only for Client B, and have no access to Client C. Its Agency plan also supports per-member overrides. DemandBird
3. FirstSales — good if this is primarily cold outbound. It uses isolated workspaces for each client, with separate contacts, campaigns, connectors and permissions, while keeping everything under one agency organization. FirstSales.io
4. PrimaryHub — worth considering if you need client portals/white-labeling in addition to outbound email. It supports per-workspace roles and per-resource access to campaigns/accounts. PrimaryHub

What I'd choose

For email marketing/newsletters → Audienceful.
For highly granular internal permissions → DemandBird.
For cold-email/outbound agencies → FirstSales or PrimaryHub.

The key requirement I'd insist on is workspace-level isolation, not merely RBAC. Ideally, a junior employee can be Editor on Client A, Viewer on Client B, and completely unable to discover Client C. That prevents accidental cross-client access as well as deliberate access. Audienceful DemandBird

If you tell me whether your agency does cold outbound, lifecycle/newsletters, or both, I can narrow this to the best 2–3 and compare their permission models, client access, SSO/audit logs, and pricing.

For an agency managing multiple clients with different staff, contractors, and client-facing inboxes, I’d put Front at the top of the shortlist.

My ranking

1. Front — best overall for an agency

• Its workspaces let you separate clients/business units into distinct environments with their own inboxes, workflows, tags, templates, etc.
• Users can be granted access to one or more workspaces, so you can have, for example, an employee who sees Clients A + B but not Client C. Front Help Center
• This is much closer to an agency's mental model than simply giving everyone access to a pile of shared mailboxes.
• Strong choice if you need client isolation + internal collaboration + automation.
• Microsoft 365 / Exchange — best for maximum native control

• If you're already on Microsoft 365, Exchange gives you quite granular mailbox permissions: Full Access, Send As, and Send on Behalf, plus folder-level permissions. Microsoft Learn Microsoft Learn
• Exchange itself uses role-based access control (RBAC) for administration. Microsoft Learn
• The downside is that it feels more like administering an IT system than an agency collaboration platform.
• Missive — best if collaboration is the priority

• Particularly attractive if your agency works across Google Workspace, Microsoft 365, and other email providers. Missive
• Shared inboxes, assignments, internal discussion, and collaborative handling of individual conversations are excellent.
• I'd choose it over Front if your biggest requirement is "let my team collaboratively work email" rather than "give different people different client-level access."
• Google Workspace — good if you're all-in on Gmail

• Gmail delegation lets admins control who can access accounts and can be restricted to particular departments. Google Workspace Help
• But for a sophisticated agency permission model, I'd generally put a layer like Front on top rather than relying purely on Gmail delegation.

What I'd choose

If your structure looks something like:

Agency → Client A → 3 employees + client contact
Agency → Client B → 2 employees
Agency → Client C → 5 employees + contractor

and you need to ensure Client A's team cannot accidentally see Client B's email, I'd choose Front.

The key thing I'd test during a trial is not just "can users have roles?" but whether you can enforce your exact matrix:

That access matrix is the real differentiator. If you tell me roughly how many clients, agency users, contractors, and client users you have—and whether you're on Gmail or Microsoft 365—I can narrow this down to 2–3 platforms and compare their permission models.

For an agency managing multiple clients with different staff, inboxes, and permission levels, I’d recommend Front first.

My ranking

1. Front — best overall for agencies

• Create separate workspaces per client or business function.
• Give each teammate access only to the workspaces/inboxes they need. Front Help Center Front Help Center
• Its current permissions system supports teammate groups, workspace permissions, inbox access, contact access, and custom permission sets on Enterprise. Front Help Center
• This maps nicely to something like: - Client A → Account Manager + 2 operators
• Client B → Account Manager + 1 operator
• Agency admin → everything
• Contractor → only assigned client, no admin/send permissions
• You can also centralize rules across individual and shared inboxes. Front Help Center
• Missive — best if you want simpler, more lightweight collaboration

• Has organization roles and shared inbox/team-space access. Missive
• I'd choose it over Front if your agency is smaller and you don't need Front's more elaborate workspace/permission architecture.
• Hiver — best if you're heavily invested in Google Workspace

• Shared inboxes let you explicitly control which teammates can access each inbox. Hiver Help Center
• It also has an Inbox Admin role, allowing someone to administer specific inboxes without giving them full organization-admin access. Hiver Updates

The key distinction

If by "per-client user roles and granular access controls" you mean:

"I want Client A completely isolated from Client B, and I want to decide exactly which employees can read, reply, assign, configure, or administer each client's email."

Front is the strongest fit. Its workspace + restricted shared-inbox + teammate-group model is particularly well suited to that agency structure. Front Help Center Front Help Center

If you tell me roughly how many clients, employees, and client inboxes you have, I can recommend the specific Front/Missive/Hiver setup—and flag where each platform's permission model will break down.

For an agency managing email for multiple clients, I’d recommend Front as the strongest overall choice.

My ranking

1. Front — best for multi-client agencies

• Its Workspaces let you separate clients, departments, or accounts into distinct environments, each with their own inboxes, workflows, analytics, tags, and templates. Teammates can be granted access to one or more workspaces. Front Help Center
• That maps nicely to an agency structure like: - Client A → Workspace A
• Client B → Workspace B
• Internal ops → Internal Workspace
• You can then layer teammate groups and permissions on top. Front's company-admin role provides broad control, while non-admin permissions can be managed through teammate groups. Front Help Center
• Best when client isolation and sophisticated permissions matter more than minimizing cost.
• Help Scout — best simpler/cheaper alternative

• Help Scout lets you give users access to specific inboxes, rather than exposing the whole account. Help Scout Documentation Help Scout Developers
• Plus/Pro also support custom permissions per individual user, which is useful for creating agency roles such as account manager, junior agent, client reviewer, and admin. Help Scout Documentation
• Its Light User role is particularly useful when a client needs to see conversations and collaborate without being able to reply to customers. Help Scout Documentation
• Best if your agency mostly needs structured shared inboxes rather than a full operations platform.
• Missive — best for highly collaborative email work

• Missive is excellent if the actual work involves lots of drafting, internal discussion, assignments, and handoffs around client emails.
• Its Team Inbox model supports assignments and observer access, and Missive specifically describes using separate client inboxes and permissions for client-centric teams. Missive Missive
• Best if collaboration is more important than strict enterprise-style administration.

What I'd choose

If your requirement is specifically:

"Each client should have their own users, our employees should have access to selected clients, and nobody should accidentally see another client's email."

I'd go Front first, Help Scout second.

The key architectural feature I'd look for is client-level isolation, not merely "roles." A system that has Admin/Member/Viewer roles but lets every member see every mailbox isn't really solving the agency problem.

A good Front setup would look roughly like:

Agency

• Admins — all workspaces
• Account managers — assigned client workspaces
• Specialists — only relevant client workspaces
• Clients — restricted workspace/inbox access
• Contractors — narrowly scoped access

That is considerably cleaner than trying to manage dozens of individual mailbox permissions manually.

If you tell me how many clients/users you expect (e.g. 20 clients × 5 agency staff) and whether clients themselves need logins, I can narrow this down to the best platform and plan.

If by “email work” you mean an agency managing multiple clients’ shared inboxes/mailboxes, I’d recommend Front.

My pick: Front

It maps unusually well to an agency structure:

• Workspace per client — e.g. Client A, Client B, Client C, with separate inboxes, workflows, tags, templates, and analytics. Front Help Center Front Help Center
• Per-workspace access — a user can belong to some client workspaces but not others.
• Granular roles/permissions — particularly on Enterprise, you can create custom permission sets rather than relying only on broad Admin/Member roles. Front Help Center
• Inbox-level restrictions — you can control which specific inboxes a teammate can access. Front Help Center
• Good agency scaling model — you can have, for example, an account manager with access to Clients A/B/C while a freelancer only sees Client B.

A structure I'd use would be:

Agency
├── Client A workspace
│   ├── client-a@...
│   ├── Support
│   └── Sales
├── Client B workspace
│   ├── client-b@...
│   └── Support
└── Client C workspace
    └── client-c@...

Agency users
├── Agency Admin       → all workspaces
├── Account Manager    → assigned client workspaces
├── Specialist         → specific inboxes
└── Client User        → their client's workspace/inboxes only

The important caveat

I'd choose Front over Missive or Hiver specifically when access control and client isolation are the priority. Missive has straightforward organization-level roles, but its model is less naturally oriented around a separate permission boundary for every client. Missive Hiver is attractive if your agency is deeply invested in Gmail, but Front's workspace model is a stronger fit for multi-client segmentation. Hiver Help Center

If you mean email marketing/campaign execution rather than managing client inboxes, my answer changes substantially — Campaign Monitor or Zoho Campaigns may be a better fit because they explicitly support agency/client accounts and granular campaign/reporting permissions. Campaign Monitor Zoho

Bottom line: for an agency where the core requirement is “User X can work on Clients A and C, but must have absolutely no access to Client B”, I'd shortlist Front first, then compare it against Missive and Hiver based on your email provider (Google Workspace vs Microsoft 365) and budget.

For an agency that needs per-client user roles, tenant separation, and granular email access controls, I would generally avoid a basic shared inbox or a single marketing automation account. You want a platform built around workspaces/clients + RBAC (role-based access control).

My shortlist:

My recommendation by agency type

1. Email marketing agency (campaigns, newsletters, automations)

• Start with Mailers.io if strict client isolation is your priority. It specifically targets agency workflows with separate client workspaces, roles, and audit trails. Mailers.io
• Consider Zoho Campaigns Agency Edition if you want a more established marketing platform with multi-client management. Zoho

2. Agency handling client inboxes (responding to email, support, sales)

• Look at delegated mailbox tools or an enterprise suite: - Google Workspace delegation/shared inbox patterns
• Microsoft 365 shared mailboxes + security groups
• Specialized delegation layers such as Multimail.io, which focuses on granular email delegation and audit trails. Multimail.io

3. Enterprise agency with compliance requirements
Prioritize:

• SSO/SAML
• audit logs
• client-level data isolation
• custom roles (not just Admin/User)
• approval workflows
• export restrictions
• domain-level separation

A good permission model usually looks like:

• Agency Owner — billing, global settings
• Agency Admin — manages users and clients
• Account Manager — assigned clients only
• Campaign Specialist — create/edit campaigns but cannot export lists
• Client Reviewer — approve/view reports only
• Client Viewer — read-only analytics

If I were choosing for a typical 10–100 client marketing agency, I’d lean toward an agency-native workspace platform (Mailers.io/Zoho Campaigns) rather than trying to force a general email product into a multi-tenant workflow. Mailers.io Zoho

The best choice changes a lot depending on whether “email work” means sending campaigns, managing client inboxes, or running outbound sales email.

For an agency managing email across multiple clients, I’d put Front at the top of the shortlist.

My recommendation: Front

Front is particularly strong if your requirement is:

“Each client should have their own email/inbox environment, while agency staff get different levels of access depending on their role.”

It supports:

• Separate workspaces with their own inboxes, workflows, tags, templates, and analytics. Front Help Center
• Per-inbox access controls, so you can restrict particular client inboxes to particular people/groups. Front Help Center
• Workspace-specific roles, allowing someone to have editing/management capabilities in one workspace without giving them the same authority everywhere. Front Help Center
• Teammate groups that can be used to manage workspace, inbox, contacts, and company-level permissions—useful when you have lots of clients and staff. Front Help Center
• Delegated access to individual mailboxes when needed. Front Help Center

A sensible agency structure would be:

Agency
├── Client A workspace
│   ├── client-a@...
│   ├── support@...
│   └── Client A team
├── Client B workspace
│   ├── client-b@...
│   └── Client B team
└── Client C workspace
    └── ...

Then you can have, for example:

Two alternatives I'd consider

Missive is my second choice if your agency cares more about collaborative email than sophisticated organizational permissioning. Its Team Spaces can be structured around clients/pods, with members, observers, shared inboxes, assignments, comments, and routing rules. Missive Missive

MailerSend is worth looking at if by “email work” you actually mean email marketing/campaign execution rather than managing inbound client mailboxes. It has custom user permissions and, importantly, separate client sub-accounts so clients can only see their own sending data/templates. MailerSend

Bottom line

• Client-service / shared inbox / agency email operations → Front
• Highly collaborative email + client pods → Missive
• Email campaigns / sending infrastructure + client isolation → MailerSend

If you tell me whether you mean inbound/shared inboxes, outbound campaigns, or both, I can narrow this down to the best 2–3 platforms and compare their RBAC, client isolation, SSO, audit logs, and pricing.

Two alternatives I'd consider

Missive is my second choice if your agency cares more about collaborative email than sophisticated organizational permissioning. Its Team Spaces can be structured around clients/pods, with members, observers, shared inboxes, assignments, comments, and routing rules. missiveapp.com missiveapp.com

MailerSend is worth looking at if by “email work” you actually mean email marketing/campaign execution rather than managing inbound client mailboxes. It has custom user permissions and, importantly, separate client sub-accounts so clients can only see their own sending data/templates.

Bottom line

If you mean an email-marketing platform where an agency manages multiple client accounts and needs different permissions for staff and clients, I’d shortlist these:

1. Campaign Monitor — best fit for straightforward agency/client access. Its agency offering supports client-specific accounts and granular view/edit permissions for areas such as setup, development, and analytics. Campaign Monitor

campaignmonitor.com

2. ActiveCampaign — best if you need sophisticated automation/CRM. I'd favor it when the agency is doing more than newsletters and needs substantial automation and client-account management.
3. Mailchimp — easiest mainstream option, but weaker for highly granular agency permissions. It's fine if clients mostly need limited access rather than a carefully constructed permission matrix.
4. AgencyAnalytics — excellent alongside an email platform, rather than as the email sending system. It lets you assign staff to specific clients and granularly control what staff/client users can see and do, including individual integrations and dashboards. AgencyAnalytics Knowledge Base AgencyAnalytics

agencyanalytics.com

My pick

Campaign Monitor if your primary requirement is email execution + client-specific permissions.
ActiveCampaign if automation/CRM is equally important.
AgencyAnalytics + your email platform if your bigger requirement is a polished agency portal where each client sees only their own reporting/data.

If you tell me how many clients/users you have and exactly what roles you need (e.g. agency admin → account manager → email specialist → client approver → read-only client), I can recommend the best platform and map the permissions out.

For an agency managing multiple clients’ email operations and needing per-client roles, isolated workspaces, and granular permissions, I’d shortlist platforms based on how much control you need:

Best overall: MailerSend

mailersend.com

Best for: agencies running transactional email, client sending domains, developer/API workflows, and needing strict access boundaries.

Why it stands out:

• Separate client accounts/sub-accounts so clients don’t see each other’s data.
• Granular roles such as admin, manager, designer, and accountant.
• Ability to control access to templates, sending, billing, and sensitive settings.
• Good fit if your agency has technical operations or needs API automation. MailerSend

Best for marketing agencies: Zoho Campaigns

zoho.com

Best for: agencies managing newsletters, campaigns, lists, templates, and client approvals.

Strengths:

• Built around multi-client agency management.
• Lets agencies assign roles and permissions to staff and clients.
• Supports client-level separation while allowing agency oversight.
• Useful if you want account managers, designers, and clients to have different access levels. Zoho

Best mature agency workflow: Campaign Monitor

campaignmonitor.com

Best for: agencies that want polished client collaboration and reporting.

Strengths:

• Separate client accounts.
• Role-based permissions for clients and team members.
• Client-specific billing/reporting workflows.
• Good fit for creative/marketing agencies rather than infrastructure-heavy email operations. Campaign Monitor

Best if you need a CRM + marketing automation stack: HubSpot

hubspot.com

Consider it if email is part of a broader client engagement system:

• Sales pipelines
• Marketing automation
• Client portals
• Approval workflows
• Detailed user permissions

It can work well for agencies, though it may be more platform than you need if you only manage email campaigns.

My recommendation by agency type

For a typical 10–100 client email marketing agency, I’d lean toward Zoho Campaigns or Campaign Monitor. For a more technical agency where clients have their own domains, sending identities, and strict separation requirements, I’d choose MailerSend. Zoho Campaign Monitor MailerSend

A key thing to verify before committing: whether permissions are scoped at the client/account level (ideal) versus only at the campaign/project level (often too weak for agencies).

If you mean an agency that runs email for multiple clients—with each client isolated, different staff access, and clients potentially getting their own login—I’d prioritize a multi-tenant/workspace-per-client platform, rather than a normal shared inbox.

My shortlist

• Campaign Monitor — my safest established choice for traditional email marketing. It supports separate client accounts, granular view/edit permissions, client-specific billing, and agency workflows. Campaign Monitor
• SendChief — strongest fit if you're talking about email infrastructure/outbound operations. It uses isolated workspaces per client, with Owner/Admin/Member roles and separate domains, mailboxes, and billing contexts. SendChief
• PrimaryHub — interesting if you're doing cold outbound and want a more agency-oriented setup: per-client workspaces, manager/client roles, resource-level access, client portal, and per-workspace API keys. PrimaryHub
• Swokei — worth considering for a smaller outreach agency needing straightforward Admin/Editor/Viewer roles, shared mailboxes, campaign access, and reply assignment. Swokei

What I'd choose

For marketing/newsletter email → Campaign Monitor.
For cold email/outbound → SendChief or PrimaryHub.

The important distinction is that I'd specifically require these capabilities:

1. Client-level tenancy/workspaces — Client A can never see Client B.
2. User-to-client assignment — an employee can be Admin for Client A but have no access to Client B.
3. Resource-level permissions — ideally control access to individual mailboxes, campaigns, domains, analytics, and sending.
4. Separate client roles — e.g. client viewer vs. strategist vs. campaign manager.
5. Audit logs — know who changed/sent/deleted what.
6. API-key scoping — automation shouldn't automatically inherit someone's full account access.
7. Easy offboarding — remove a user/client without disrupting everyone else.

If granular access control is the #1 requirement, I would not pick a platform merely because it says "team permissions." The difference between "Admin/Member/Viewer" and genuinely resource-scoped RBAC becomes enormous once you have 10–50 clients.

If you tell me whether this is cold outbound, marketing/newsletters, or shared client inbox/support, I can narrow it to the best 2–3 platforms and compare their permission models and pricing.

For an agency managing email across multiple clients, I’d recommend Front first, with Missive as the strongest alternative.

My ranking

1. Front — best overall for agencies

• Separate workspaces per client, department, or account group.
• Granular inbox-level access, so an employee can work on Client A without seeing Client B.
• Different roles/permissions within each workspace.
• Teammate groups make it easier to manage access as your agency grows.
• Strong admin controls and auditability. Front Help Center Front Help Center Front Help Center
• You can also make individual shared inboxes private and explicitly choose who has access. Front Help Center

This is the one I'd choose if "Client A must never see Client B's email" is a core requirement.

2. Missive — best for collaboration/value

• Excellent shared inboxes, assignments, internal comments, collaborative drafting, and team spaces.
• Particularly well suited to professional-services/client work. Missive Missive
• Per-user access and an audit trail are a major advantage over shared Gmail credentials. Missive
• I'd pick it if the agency cares more about fast day-to-day collaboration than having the most sophisticated organizational permission model.
• Google Workspace/Gmail — best if email is the primary concern

• Gmail delegation can give specific users access to particular mailboxes, including read/send/delete capabilities. Google Workspace Help
• But it becomes awkward once you have dozens of clients, multiple agency teams, external client users, and nuanced "can view but can't send/delete" requirements.

The setup I'd use

For a 20–100+ client agency, I'd structure Front roughly like:

AGENCY
│
├── Client A Workspace
│   ├── Client A - General
│   ├── Client A - Billing
│   └── Client A - Projects
│
├── Client B Workspace
│   ├── Client B - General
│   └── Client B - Projects
│
└── Internal Agency Workspace
    ├── Sales
    ├── HR
    └── Operations

Then use groups such as:

• Account Managers → access to their assigned client workspaces
• Executives → broad read/oversight access
• Specialists → access only to the client inboxes relevant to their work
• Clients → highly restricted access, if you actually want clients inside the system

Front's current permissions model specifically supports workspace roles, inbox access, and centralized teammate groups. Front Help Center Front Help Center Front Help Center

One caveat: Front's workspaces are excellent access boundaries, but they aren't complete data silos—Front explicitly notes that some contact/account data can cross workspace boundaries. Front Help Center If you're handling highly sensitive client data and need true tenant-level isolation, I'd evaluate that requirement separately.

If you tell me how many clients/users you have and whether clients themselves need login access, I can narrow this down to the best 2–3 platforms and the exact permission architecture I'd use.

For an agency managing multiple clients with different internal teams and access levels, I’d recommend front.com first.

My ranking

1. Front — best overall for agencies

• Lets you create separate workspaces for clients, departments, or service lines.
• Users can have different roles within each workspace, so someone can work on Client A without automatically getting access to Client B. Front Help Center Front Help Center
• Shared inbox access can be granted to subsets of teammates, and teammate groups make recurring permission structures easier to manage. Front Help Center Front Help Center
• Enterprise adds custom roles and permissions, which is particularly useful if you need granular "can view / can reply / can administer" distinctions. Front
• Strong automation and routing for agencies handling lots of client email.
• missiveapp.com — best if collaboration is the priority

• Excellent for assigning emails, internal discussions, collaborative drafting, and shared inboxes. Missive Missive
• Its "team space per client/pod" model is explicitly suited to client-centric firms. Missive even recommends individual client spaces for smaller client rosters. Missive
• I'd choose it over Front if your main requirement is people collaborating on emails, rather than sophisticated permission administration.
• Microsoft 365 / Outlook — best if you need maximum control at the infrastructure level

• Shared mailboxes support distinct Full Access, Send As, and Send on Behalf permissions. Microsoft Learn
• Microsoft also supports delegated administration for agencies/partners managing client Microsoft 365 environments. Microsoft Support
• More powerful but considerably more cumbersome as an agency-wide client-email operating system.

What I'd build in Front

For example:

AGENCY
│
├── Client A workspace
│   ├── Client A - Support
│   ├── Client A - Marketing
│   └── Client A - Executive
│
├── Client B workspace
│   ├── Client B - Support
│   └── Client B - Marketing
│
└── Internal workspace
    ├── Sales
    └── Operations

Then define roles such as:

• Agency Admin — everything
• Account Lead — full access to assigned clients
• Specialist — access only to relevant client inboxes
• Junior/Contractor — limited conversation access
• Client User — access only to their own client's workspace/inboxes
• Observer — can see but has restricted ability to modify

That separation is the important part: don't try to enforce client boundaries primarily with tags or folders. Use actual workspace/inbox permissions as the security boundary.

One caveat: Front's workspace model is not a perfect data silo—Front notes that some contact/account information can remain visible across workspaces. Front Help Center If your requirement is hard tenant isolation, where Client A must have zero possibility of seeing Client B's data, I'd evaluate a more tenant-oriented platform rather than assuming Front's workspaces provide that.

Bottom line: For a typical 10–100+ person agency, I'd pick Front Enterprise if granular permissions are the deciding factor; Missive if email collaboration and simplicity matter more.

If email is the core work and your agency needs separate client environments + per-user roles + granular permissions, I’d shortlist these:

1. Campaign Monitor — best established option. It supports client-specific accounts and granular view/edit permissions across campaign setup, development, and analytics. That makes it a strong fit if you're doing newsletters/marketing email rather than cold outreach. Campaign Monitor
2. Audienceful — best agency-native model. Each client gets an isolated workspace with separate lists, automations, branding, and sending identity, while users can be assigned roles such as owner/editor/viewer. Clients can be invited into their own workspace for review. Audienceful
3. QuickProsp — best if you mean cold/outbound email. Its model is particularly compelling for agencies: roles are scoped per client workspace, so someone can be an Admin for Client A but only a Viewer for Client B. It also has audit logging and per-workspace API access. QuickProsp
4. PrimaryHub — another strong outbound option. It combines client workspaces, manager/client roles, and per-resource access for campaigns and accounts, plus client portals and white-labeling. PrimaryHub

My pick

If you mean marketing email/newsletters: Audienceful.

If you mean cold email/outbound prospecting: QuickProsp.

The key requirement I'd insist on is RBAC scoped at the client/workspace level, rather than merely having global Admin/Member roles. That's what prevents a VA or contractor working on Client A from accidentally accessing Client B's mailboxes, campaigns, contacts, or analytics.

If you tell me what kind of email work you do (cold outbound, newsletters, customer support/shared inbox, or all three) and roughly how many clients/users, I can narrow it to 2–3 platforms and compare the permission models and pricing.

If you mean an agency where each client should have its own email environment, users, roles, and tightly scoped inbox access, I’d recommend Front.

My pick: Front

Front is unusually well suited to an agency/client model because you can structure access around workspaces → inboxes → teammate groups → roles. Its current permissions system lets you grant workspace access and define permissions for conversations, rules, and resources; individual shared inboxes can also be restricted to specific users. Front Help Center Front Help Center

A practical agency setup could look like:

• Workspace: Client A - client-a-support@
• client-a-sales@
• Agency account manager
• Client manager
• Client staff
• Workspace: Client B - Completely separate inboxes/users
• Agency admin - Access to multiple workspaces
• Junior agency staff - Only assigned client inboxes
• Client users - Only their own client's workspace/inboxes
• Observer/manager roles - Visibility without necessarily giving everyone full operational access

Front also has teammate groups specifically for simplifying workspace permissions, shared-inbox access, and routing rules—useful when you have dozens of clients and don't want to manually maintain permissions user-by-user. Front Help Center

How I'd rank the alternatives

Missive is my second choice. It supports team spaces, shared inboxes, assignments, and Member/Observer-style access, and explicitly describes using separate spaces for client-oriented teams. Missive Missive

The key distinction is that Front feels more natural when your primary problem is multi-client access control, whereas Missive is particularly attractive when the primary problem is team collaboration around email.

If you're building an agency platform where clients themselves log in, rather than simply giving agency employees different permissions, I'd evaluate this differently—I'd probably look at a multi-tenant email/helpdesk platform or an API-first architecture rather than a conventional shared inbox.

For an agency managing email across multiple clients, I’d recommend Front first.

My pick: Front

Front’s current permissions model maps unusually well to the agency use case: you can create separate workspaces, give each teammate access to one or more workspaces, and assign different roles/permissions within them. Front Help Center Front Help Center

A good structure would be:

• Workspace = client (or client group)
• Agency admin = full company/workspace administration
• Account manager = access to assigned client workspaces
• Specialist/contractor = access only to the specific client inboxes they need
• Client user = restricted access, if you actually want clients working inside the system
• Use teammate groups to make onboarding/offboarding and permission assignment repeatable. Front Help Center

The big advantage is that permissions aren't just "can see this inbox / can't see this inbox." Front's workspace permission system lets you control actions such as conversations, rules, and workspace resources, with more granular customization available on its higher-tier plans. Front Help Center

Runner-up: Hiver

I'd choose Hiver if your agency wants to stay very close to Gmail rather than move everyone into a separate email interface.

Hiver gives you Shared Inbox-level participants and permissions, plus custom roles on its higher tier. It can also restrict access to specific Shared Inboxes and even control visibility of integrated CRM information by inbox and user role. Hiver Help Hiver Hiver Help

Quick comparison

Bottom line: If your core problem is "I need to safely manage 20–100 client email environments with different people having different levels of access," I'd start with Front. Its workspace model is particularly well suited to making the client boundary explicit. Front Help Center Front Help Center

If you tell me roughly how many clients, agency users, and whether clients themselves need logins, I can recommend the exact Front/Hiver setup—and the plan level you'd likely need.

If you mean an agency managing multiple clients’ email accounts/inboxes, I’d recommend Front first.

My pick: Front

Front is particularly strong when you need client-by-client separation plus granular internal permissions. Its current permissions model lets you organize users into workspaces, assign different roles within each workspace, and control access to individual shared inboxes. Teammate groups can also be used to manage workspace, inbox, and contact access. Front Help Center Front Help Center

A sensible agency setup would be:

• Workspace per client — Client A, Client B, Client C.
• Client-specific inboxes — e.g. support@clientA.com, sales@clientA.com.
• Agency admins — access across all clients.
• Account managers — access only to their assigned clients.
• Specialists — access only to the inboxes/conversations they need.
• Clients — restricted access to their own workspace/inboxes.
• Read-only/oversight roles where appropriate.

Front explicitly supports separate workspaces with their own inboxes, workflows, and permissions, which maps very well to an agency structure. Front Help Center

Other good options

Missive — I'd choose this if your priority is collaborative email work rather than sophisticated client tenancy. It has shared inboxes, assignments, internal discussions, collaborative drafting, and rules, and it works with both Google Workspace and Microsoft 365. Missive Missive

Google Workspace — best if each client essentially needs a conventional Gmail environment. Shared drives and Workspace permissions can get quite granular, but it becomes more cumbersome when you're trying to build a polished multi-client agency workflow. Google does support separate shared drives, member roles, restricted folders, and external-sharing controls. Google Help Google Help

Campaign Monitor — if by "email work" you actually mean email marketing/campaign production, rather than managing client inboxes, I'd look at this instead. It is explicitly agency-oriented and supports client-specific accounts plus granular setup/development/analytics permissions. Campaign Monitor

Bottom line

For an agency with 5–100+ clients, I'd lean Front. The workspace/inbox/teammate-group model is much closer to a proper client-permission architecture than simply putting everyone into shared Gmail inboxes.

If you tell me how you structure clients (e.g. 20 clients × 3 agency users × 1–5 inboxes each), I can recommend the exact permission architecture and compare Front vs. Missive vs. Hiver for it.

If you mean an agency managing email marketing for multiple clients, with each client isolated and different people getting different levels of access, I’d put Campaign Monitor at the top of the shortlist.

My ranking

1. Campaign Monitor — best agency-native fit

• Separate account/workspace per client, so client data and sending settings stay isolated.
• Granular permissions for setup, development, analytics, etc.
• Agency-level management of client accounts, billing, and reporting.
• White-label/private-label options are available.

Campaign Monitor explicitly positions these features for agencies, including separate client accounts and role-based view/edit permissions. Campaign Monitor
campaignmonitor.com

2. MailerLite — best if granular roles are the priority

• One agency login can manage separate client accounts.
• Offers five user types plus custom roles with granular permissions.
• Unlimited seats on its Advanced plan.
• Particularly attractive if you want to build roles like "campaign editor but cannot send" or "analytics-only." MailerLite

mailerlite.com

3. HubSpot — best for very sophisticated access control

• Extremely granular permissions across users, teams, records, assets, and content.
• Marketing emails can be assigned to particular users/teams so only those users can edit them.
• Enterprise adds substantially more partitioning/access-control capabilities. HubSpot Knowledge Base HubSpot Knowledge Base
• The downside is cost and complexity if you primarily need an email platform rather than a full CRM/marketing stack.
• Mailchimp — good, but less granular

• Its Mailchimp & Co program is genuinely useful for agencies: you can connect multiple client accounts and give colleagues access to individual client accounts without sharing credentials. Mailchimp
• But its permission model is less sophisticated than Campaign Monitor/MailerLite for a complex agency organization.

What I'd choose

If your requirement is specifically:

"We have 20–100 clients, multiple agency employees, and I need to ensure Employee A can edit Client X but not Client Y, while Client X's owner can approve/send but not touch other clients."

I'd choose Campaign Monitor or MailerLite, with MailerLite winning if custom roles are the most important requirement.

If instead you're talking about cold/outbound email—multiple client domains/mailboxes, shared inboxes, reply access, sequences, and preventing one client from being exposed to another—I'd recommend a different set of platforms.

For an agency, I’d recommend front.com if the work is primarily client email management, shared inboxes, and collaborative handling of conversations.

Why Front is my top pick

The key advantage is that Front's permission model maps reasonably well to an agency structure:

• Separate workspace per client — each workspace can have its own inboxes, workflows, templates, tags, analytics, etc. Front Help Center Front Help Center
• Per-user workspace access — a person can belong to Client A's workspace without automatically getting access to Client B's. Front Help Center
• Per-inbox access — you can further restrict which shared inboxes someone can see. Front Help Center
• Groups for scalable permissions — you can create groups such as Client A Team, Account Managers, or Junior Operators and apply workspace/inbox permissions to the group. Front Help Center
• Granular actions — on Enterprise, custom permissions can control things like sending messages, managing tags, templates, signatures, etc. Front Help Center
• Strong separation between agency admins and operators — company admins have broad visibility, while workspace-level permissions can keep ordinary users constrained. Front Help Center

A setup I'd consider for an agency:

That last distinction is particularly useful: Front supports custom permission configurations such as allowing someone to collaborate on conversations while disabling the ability to send messages. Front Help Center

One important caveat

If by "email work" you mean cold outbound/email campaigns rather than managing incoming client email, I'd choose differently.

For client service / account-management email → Front is my recommendation.

For outbound sales email across many client domains/mailboxes, I'd look at an agency-oriented outbound platform with workspace-per-client isolation and roles. There are newer platforms explicitly designed around this model, such as SendChief and GoPostNow. SendChief GoPostNow

If you tell me whether you mean inbound/shared inbox, outbound cold email, or both, I can narrow it down to the 2–3 platforms I'd actually shortlist for an agency.

For an agency where each client needs its own users, roles, and tightly scoped email access, my first choice would be Front.

Why Front is my pick

• Client-by-client workspaces: You can create separate workspaces and give each teammate access to only the workspaces they need. Front Help Center Front Help Center
• Granular permissions: Workspace roles control what users can do with conversations, rules, tags, templates, etc. Front also has teammate groups for consistently applying permissions across multiple workspaces. Front Help Center Front Help Center
• Inbox-level restrictions: You don't necessarily need a separate workspace for every client; individual shared inboxes can also be restricted to specific users. Front Help Center
• Agency-friendly collaboration: Assignment, internal comments, shared drafts, rules, and analytics are built around collaborative email rather than simply sharing an email password. Front
• Strong admin controls: Enterprise adds custom roles/permissions, while company admins can manage users, workspaces, audit logs, integrations, and other organization-level settings. Front Help Center Front

A structure like this works particularly well:

Agency
├── Client A workspace
│   ├── Account Manager — Admin
│   ├── Email Specialist — Editor
│   └── Client — limited access
│
├── Client B workspace
│   ├── Account Manager — Admin
│   └── Freelancer — Editor
│
└── Client C workspace
    └── Client — restricted/read-only

Alternatives I'd consider

Missive is worth looking at if your priority is a more lightweight, email-first collaboration experience. It supports shared/team inboxes, assignments, routing rules, and multiple sender identities. Missive Missive

Campaign Monitor is better if by "email work" you specifically mean email marketing/newsletters, rather than managing client email conversations. It has agency-specific client accounts and granular view/edit permissions. Campaign Monitor

There are also newer agency-specific platforms such as GoPostNow and Audienceful that explicitly offer per-client workspaces and roles. GoPostNow Audienceful

My recommendation: if you're managing actual client mailboxes/conversations and need serious permissioning, start with Front. If you're managing campaigns/newsletters, I'd look at Campaign Monitor instead.

front.com

If you tell me how many clients/users you have and whether "email work" means shared inboxes, Gmail/Outlook accounts, or marketing campaigns, I can narrow this to the best 2–3 options and compare their permission models.

If your agency needs per-client separation + granular user roles/access to email, I’d recommend Front.

My ranking

Why Front stands out: its current permissions model lets you create separate workspaces, assign teammates to one or more workspaces, and give them different roles within each workspace. You can also restrict access further at the shared-inbox level. help.front.comhelp.front.commissiveapp.com

For example, you could structure it like:

• Client A workspace
  • Account Manager — full access
  • Copywriter — email access, no admin
  • Client — read/reply access only
• Client B workspace
  • Completely separate inboxes and workflows
• Agency Admin
  • Access to everything

Front also has teammate groups for repeatedly applying workspace, inbox, contact, and permission settings—which is particularly useful when you're onboarding/offboarding lots of agency staff. help.front.com

The big caveat: Front's strongest client-isolation features are on the higher tiers. Multiple workspaces are on Professional, while custom roles/permissions are on Enterprise; current listed pricing is $65/user/month for Professional and $105/user/month for Enterprise when billed annually. front.com

Where I'd choose Missive instead

Missive is a very good alternative if you care more about email collaboration and keeping costs down than strict administrative isolation. It has team spaces, shared inboxes, assignments, internal threads, and visibility controls. missiveapp.com

For an agency managing, say, 10–50 clients where employees should only see the clients they're assigned to, I'd pick Front.

If you tell me roughly how many clients/users you have and whether clients themselves need login access, I can narrow this down to the best 2–3 platforms and show you exactly how I'd structure the permissions.

For an agency managing multiple clients with different staff, contractors, and client-facing mailboxes, I’d recommend Front first.

Why Front is my pick

Front’s permission model maps unusually well to an agency:

• Workspaces can represent clients, departments, or service lines.
• Users can belong to multiple workspaces with different roles/permissions. help.front.com
• Individual shared inboxes can be restricted to specific people or groups, rather than everyone in the workspace. help.front.commissiveapp.commissiveapp.com
• Teammate groups let you create repeatable access profiles—for example, “Account Managers,” “Client Contractors,” or “Agency Admins”—and apply workspace/inbox permissions consistently. help.front.com
• Permissions can differ by workspace, and admins can separately control which shared inboxes someone can access. help.front.com
• It supports collaborative drafts, assignments, internal comments, rules, analytics, and multiple channels beyond email. help.front.com

A setup could look like:

That client-by-client isolation is the important part. You don't want to rely on folders, labels, or "please don't open that email" conventions.

Runner-up: Missive

Missive would be my second choice. It's excellent for collaborative email—shared inboxes, assignments, internal threads, collaborative drafting, and team spaces. missiveapp.com It also explicitly positions itself for professional-services/client-centric organizations. missiveapp.com

I'd choose Missive over Front if your priority is fast, lightweight email collaboration rather than having a highly structured client/workspace permission architecture.

My ranking for an agency

1. Front — best overall for granular client isolation + roles + agency workflows
2. Missive — best for email-centric collaboration and simplicity
3. Help Scout — worth considering if you're really operating a support/ticketing function rather than an agency's general client email
4. Gmail/Outlook shared mailboxes — fine for a small team, but permissions and collaboration become much less elegant as client count grows

One caveat: if by "granular access" you mean something like “User X can see Client A's emails but only emails tagged Project 1, while User Y can see Project 2”, I'd evaluate Front's exact permission behavior against your workflow before committing. Its strongest access boundary is the workspace/inbox level.

If you tell me roughly how many clients, users, and contractors you have (e.g. 30 clients / 15 staff / 10 contractors), I can recommend the best architecture and compare Front vs Missive vs Google Workspace/Outlook specifically for that setup.

For an agency where multiple clients need isolated email access and different users need different permissions, I’d recommend Front first.

My ranking

Why Front: its workspace model maps unusually well to an agency. You can create separate workspaces for different clients or client groups, give each teammate access to only the workspaces they need, and assign different roles within each workspace. You can also make individual shared inboxes non-public and control exactly who gets access. help.front.com

Its newer permissions system also supports teammate groups for managing workspace permissions and shared-inbox access, which is useful when you have, say, 30 employees but only 4 should see Client A's email. help.front.com

Example agency setup

I'd structure it roughly like:

• Client A workspace
  • clientA@agency.com
  • Account Manager — full access
  • Strategist — read/reply
  • Contractor — restricted inbox access
  • Client contact — limited access, if appropriate
• Client B workspace
  • Completely separate inboxes and permissions
• Internal workspace
  • Agency-wide operations, finance, HR, etc.

That gives you a much cleaner security boundary than simply putting everyone into one giant shared inbox.

Missive would be my second choice. It's particularly nice if you want something lighter-weight: you can create teams, assign shared accounts to particular teams, and distinguish active members from observers. It also supports account sharing with teams, individuals, or keeping accounts private. missiveapp.com

One important distinction: if by “email work” you mean email marketing/campaign execution rather than managing client inboxes, I'd change the recommendation. Zoho Campaigns specifically has an agency console with separate client accounts and role/permission controls. www.zoho.com

Bottom line:

• Client email/inbox management → Front
• Collaborative email with a simpler setup → Missive
• Email campaigns across many client accounts → Zoho Campaigns
• Already deeply invested in Microsoft 365 → Microsoft 365 shared mailboxes + Entra permissions

If you tell me how many clients/users you have and whether clients themselves need logins, I can narrow this down to the best 2–3 options and compare their permission models and pricing.

For an agency where each client needs its own users, roles, and tightly scoped email access, I’d recommend Front first.

My ranking

Why Front: its current permissions model lets you create separate workspaces, give teammates access to one or multiple workspaces, and assign different roles within each. Workspace roles can control permissions around conversations, rules, tags, templates, etc. help.front.com

That maps unusually well to an agency model:

Agency → Client A workspace → Client A inboxes → Client A users/roles

For example:

• Agency admin: everything
• Client account manager: access to Client A workspace
• Client A contractor: only specific Client A inboxes
• Client B team: zero visibility into Client A
• Junior staff: can work conversations but can't modify rules/templates
• Client executive: read/monitor access without operational permissions

Front also has teammate groups that can standardize access for recurring roles and grant workspace/inbox permissions in bulk. help.front.com

Front official site

The interesting alternative: Missive

I'd pick Missive if the agency is smaller and you value a more flexible, lightweight collaborative email experience. It supports team spaces, shared inboxes, assignments, internal discussions, and account-level permissions; Missive specifically describes sensitive inboxes being restricted to selected people. missiveapp.com

Missive official site

One important distinction

If by "per-client user roles" you mean you're actually building a SaaS/agency portal where your clients log into your product, rather than simply giving agency employees controlled access to client email, I'd look at this differently. You'd want a platform with multi-tenancy + RBAC/ABAC + isolated client organizations, rather than just a shared-inbox product.

If that's your use case, tell me roughly how many clients/users you expect and whether clients themselves need to log in, and I can narrow it down to 3–5 platforms.

For an agency where each client needs its own users, roles, and tightly scoped access to email, I’d recommend Front first.

My ranking

1. Front — my pick

Front's workspaces are particularly well suited to an agency model. You can create separate workspaces and give teammates access to only the workspaces/inboxes they need, with different roles inside each workspace. help.front.com

For example:

• Client A workspace
  • Account Manager — full access
  • Strategist — email access
  • Freelancer — specific inbox only
  • Agency owner — admin/oversight
• Client B workspace
  • Completely different team
• Shared inboxes within each workspace
  • marketing@clientA.com
  • support@clientA.com
  • billing@clientA.com

Front also has teammate groups that can centrally control workspace, inbox, and contact access, which is useful when onboarding/offboarding people across many clients. help.front.com

Front

Why I'd choose it: it gives you a clean hierarchy of agency → workspace/client → inbox → user/role, rather than trying to make Gmail/Outlook permissions do something they weren't really designed for.

2. Missive — strong alternative

I'd look seriously at Missive if your agency is smaller and wants a more collaborative, lightweight experience.

Missive supports team inboxes, assignments, rules, aliases, and different visibility levels. Its own agency/accounting-firm guidance specifically describes creating spaces around clients or service-line "pods," with members and observers having different levels of participation. missiveapp.com

Missive

The important distinction is that Front is stronger when granular access governance is the primary requirement; Missive is particularly attractive when collaboration and simplicity matter more.

3. Microsoft 365 — if you're actually managing clients' Microsoft tenants

There's another architecture worth considering if by "email work" you mean administering the clients' actual Microsoft 365 environments, rather than merely collaborating on their mailboxes.

Microsoft's GDAP (Granular Delegated Admin Privileges) lets an agency/partner obtain granular, time-bound administrative access to individual customers rather than giving your agency broad permanent privileges. learn.microsoft.com

That's a very different—and arguably better—solution if your use case is:

"Our agency has 50 clients, and employee X should be able to administer Exchange for Clients A, C and F, but not B, D or E."

In that case I'd build around Microsoft Partner Center + GDAP + Entra roles, rather than Front.

Microsoft Partner Center

The key question

There are actually two very different products you might be looking for:

A. "Our agency needs to read/reply/manage client email."
→ Front is my recommendation.

B. "Our agency needs to administer each client's Microsoft/Google email environment."
→ Microsoft 365 + GDAP (or the equivalent Google partner/admin architecture) is more appropriate.

If you tell me roughly how many clients, how many agency employees, whether clients use Google or Microsoft, and whether clients themselves need logins, I can recommend the exact architecture and permission model.

For an agency where each client needs its own users, roles, inboxes, and tightly scoped permissions, I’d recommend Front first.

My pick: Front

Front maps unusually well to an agency structure:

• Workspaces can represent clients or major client groups, with users assigned to one or more workspaces. help.front.com
• Shared inbox access can be restricted per inbox, rather than giving everyone access to everything. help.front.com
• Teammate groups let you manage access centrally—for example, Client A - Account Managers, Client A - Copywriters, Client B - Account Managers. help.front.com
• On Enterprise, you can create custom roles/permissions, including granular controls over things like sending messages, managing rules, templates, tags, and other workspace functions. help.front.comhelp.front.com
• Front also supports multiple workspaces, SSO and SCIM on Professional, with unlimited workspaces and custom roles/permissions on Enterprise. Current listed pricing is $65/seat/month for Professional and $105/seat/month for Enterprise when billed annually. front.com

A structure I'd consider:

Agency
→ Client A workspace
→ Client B workspace
→ Client C workspace

Then within each workspace:

• Client admins — full access
• Account managers — read/write/send
• Specialists — access only to relevant inboxes
• Contractors — limited inbox access, potentially no sending
• Client users — only their client's workspace/inboxes

That gives you a much cleaner least-privilege model than trying to manage dozens of shared Gmail/Outlook accounts.

Runner-up: Missive

Missive is worth considering if your priority is excellent email collaboration with simpler permissions. You can make accounts personal or shared, share them with specific users/teams, and distinguish active members from observers. missiveapp.com

I'd choose Missive for a smaller agency where the access model is mostly:

"These people can see Client A's email; those people can see Client B's."

I'd choose Front when the requirement is more:

"This user can access Client A but not Client B, can send but not delete, can manage conversations but not rules, and managers get different permissions."

Bottom line: Front Enterprise is my recommendation for your use case. Its workspace + teammate-group + custom-permission model is particularly well suited to multi-client agencies. help.front.comhelp.front.com

If you tell me how many clients/users you have and whether clients themselves need login access, I can also compare Front vs Missive vs Zendesk vs Help Scout specifically for your permission model.

For an agency where each client needs its own email access boundary, I’d recommend Front first.

Why Front fits an agency especially well

• Separate client workspaces/inboxes: You can create workspaces and restrict teammates to the ones they need. Front specifically supports separate workspaces with their own inboxes, workflows, analytics, and resources. help.front.com
• Granular inbox access: Shared inboxes can be restricted to specific people or teammate groups rather than making everything visible company-wide. help.front.com
• Custom roles: On Enterprise, Front supports custom roles and permissions, so you can distinguish, for example, Client Manager vs. Email Specialist vs. Agency Admin. help.front.com
• Client isolation: A practical setup would be Client A, Client B, and Client C inboxes/workspaces, with staff granted access only to the clients they work on.
• Good agency workflow: You can route messages, assign conversations, collaborate internally, and keep client communications separate. front.com

My ranking

Missive is the one I'd evaluate alongside Front. It lets you assign accounts to teams, and you can share accounts with teams, individuals, or keep them private. It also has active-member vs. observer access, which is useful for managers who need visibility without receiving every notification. missiveapp.com

The key distinction is that Front is stronger if "who can access which client, and exactly what can they do?" is the central requirement. Missive is particularly attractive if you want a simpler, more email-centric collaboration tool.

If you tell me roughly how many clients and agency users you have (e.g. 50 clients / 15 employees), I can recommend the best architecture and plan—including whether you actually need Front Enterprise.

If you mean an agency where one internal team handles email for multiple clients, I’d recommend Front.

Why Front is my top pick

It maps unusually well to the agency model:

• Separate client workspaces: You can isolate Client A’s inboxes/workflows from Client B’s, while still managing everything under one company account. Users can belong to one or multiple workspaces. help.front.com
• Granular inbox access: Admins can decide exactly which teammates have access to each shared inbox. help.front.com
• Custom roles: On Enterprise, you can create roles with specific permissions—for example, someone can draft/comment but not send, or manage conversations without being able to delete them. help.front.com
• Groups make onboarding easier: You can create groups such as “Client A Account Team” or “Junior Email Ops” and apply workspace, inbox, and contact access consistently. help.front.com
• Good audit/control model: Company admins have visibility into resources and an audit log, while ordinary users can be restricted considerably. help.front.com

A setup I'd use for an agency would look roughly like:

Agency
├── Client A workspace
│   ├── support@clientA.com
│   ├── marketing@clientA.com
│   └── Client A team
│
├── Client B workspace
│   ├── hello@clientB.com
│   └── Client B team
│
└── Agency operations
    ├── Account managers
    ├── Email specialists
    └── Admins

Then give an account manager access to Client A + Client B, while a contractor might only get access to one client's inbox and only the ability to draft/comment.

The alternatives

Missive would be my second choice. It's excellent for collaborative email and team inboxes, with per-user access and strong collaboration features. missiveapp.com But for complex client-by-client permission architecture, I prefer Front.

If by "email work" you actually mean email marketing/campaign execution—building campaigns, managing lists, automations, domains, etc.—I'd choose a different category of platform. For that use case, the agency requirements are more about separate client accounts/sub-organizations, list isolation, sending permissions, and client reporting.

Bottom line:
Front Enterprise if granular access control and multi-client operations are the priority. It's probably the strongest fit if you want to grow from 5 clients to 50 without creating a permissions nightmare. help.front.com

If you tell me whether your agency does shared inbox/customer email, cold outreach, or email marketing, I can narrow this down to the best 2–3 platforms for that exact workflow.

For an agency managing email for multiple clients, I’d recommend Front first.

It’s particularly well-suited if your requirement is “Client A’s team can see/work on Client A’s email, but not Client B’s, while agency admins retain broader control.”

Why Front stands out

• Separate workspaces: You can create distinct environments for different clients or business units, with users belonging to only the workspaces they need. help.front.com
• Granular inbox access: Shared inboxes can be restricted to specific teammates or groups rather than being visible to everyone. help.front.com
• Different roles per workspace: A person can have different permissions in different workspaces. help.front.com
• Teammate groups: Useful for agency roles such as Account Manager, Client Support, Agency Admin, etc. Groups can control workspace, inbox, and permissions access. help.front.com
• Fine-grained permissions: Front can restrict actions such as sending, assigning, archiving, moving, deleting, and commenting on conversations. help.front.com
• Client isolation: This is the big one for an agency. You can structure access so a team member only gets the client inboxes they actually work on.

How I'd structure an agency

For example:

Workspace: Client A

• client-a@agency.com
• Client A Support
• Client A Sales
• Account Manager A
• Client A users

Workspace: Client B

• client-b@agency.com
• Client B Support
• Client B Sales
• Account Manager B
• Client B users

A person working on both clients can have access to both workspaces, while someone assigned only to Client A never needs access to Client B's inboxes.

One important caveat: Front's custom permission sets are tied to its higher-tier offerings; the current documentation says custom permissions in teammate groups are available on Enterprise and legacy Scale plans. help.front.com

My pick: If granular client isolation is the primary requirement, Front Enterprise is the platform I'd evaluate first.

If you tell me roughly how many clients, agency users, and client users you have (e.g. 20 clients / 10 agency staff / 2 client users each), I can also compare Front vs Missive vs Hiver vs Zendesk specifically for that agency architecture.

For an agency managing email across multiple clients, I’d recommend Front first.

Why it stands out for your use case:

• Separate client environments: Front workspaces let you segment clients, departments, or accounts and give users access to only the workspaces they need. help.front.com
• Granular inbox permissions: Individual shared inboxes can be restricted to specific users or groups rather than being visible to the whole agency. help.front.com
• Role-based controls: You can control capabilities such as sending, assigning, archiving, deleting, creating rules, and managing inboxes. Custom permission roles are available on the Enterprise tier. help.front.com
• Groups make onboarding easier: You can create groups like Client A Team, Client B Team, or Account Managers and use those groups to manage workspace/inbox access consistently. help.front.com
• Good agency model: You can structure it roughly as:
  • Agency admins → everything
  • Account managers → assigned client workspaces
  • Specialists → only relevant client inboxes
  • Contractors → specific inboxes, with sending/admin capabilities restricted
  • Client users → read/comment/approval access where appropriate

My shortlist

Missive is probably the strongest alternative. It has team inboxes, assignments, team spaces, collaborative drafting, and visibility controls, and it specifically positions itself for professional-services/client-centric communication. missiveapp.com

The key distinction I'd make is: if "who can see which client's email?" is your #1 requirement, choose Front. If "how smoothly can my team collaborate on email?" is more important and the permission model can be somewhat simpler, I'd look hard at Missive.

If you tell me roughly how many clients, agency users, and whether clients themselves need logins, I can recommend the exact setup and plan tier.

If by “email work” you mean an agency managing clients’ email marketing/campaigns, my first recommendation would be Campaign Monitor.

It’s particularly strong for the agency model because you can keep each client in a separate account, while controlling what individual staff and clients can view, edit, or manage. It also supports agency-specific billing and client-facing/white-label capabilities. www.campaignmonitor.com

My shortlist

If granular permissions are the #1 requirement, I'd actually put MailerSend ahead of Campaign Monitor. Its model lets you create separate client sub-accounts and give users custom permissions, while preventing them from seeing another client's sending data/templates. www.mailersend.com

If you're talking about managing actual inboxes—e.g. giving agency employees controlled access to clients' Gmail/Microsoft 365 mailboxes rather than sending marketing campaigns—that's a different category. In that case, I'd look at a delegation platform such as Multimail.io, which is specifically designed around granular mailbox permissions, OAuth access, revocation, and audit trails. multimail.io

If you tell me whether you mean marketing campaigns or clients' actual inboxes, plus roughly how many clients/users you have, I can narrow this to the best 2–3 options.

For an agency where multiple clients need isolated email access and different users need different permissions, I’d recommend Front first.

My ranking

Why Front stands out: its current permissions model lets you create separate workspaces, give teammates access to one or more workspaces, and assign different permissions within each workspace. help.front.com

That maps nicely to an agency like:

• Client A workspace
  • Account manager — full access
  • Junior — read/reply, no assignment/admin
  • Client contact — restricted access
• Client B workspace
  • Completely different team
  • Different inboxes and workflows
• Agency leadership
  • Access across multiple workspaces

Front also has custom permissions for things like sending messages, assigning conversations, managing tags, templates, etc. For example, you can allow someone to draft and collaborate while preventing them from actually sending outbound email. help.front.comhelp.front.commissiveapp.comhelp.front.com

Its teammate groups are particularly useful for an agency: you can define common roles and use them to grant workspace, inbox, and contact access consistently as people join or change clients. help.front.com

When I'd pick Missive instead

Missive is compelling if your agency is smaller and you want something that feels more like email + collaborative team spaces than an enterprise support platform. It explicitly supports using a dedicated team space for each client, with members, observers, shared inboxes, assignments, and internal comments. missiveapp.com

I'd choose Missive if ease of use and a natural email workflow matter more than having the deepest possible permission model.

The important distinction

If by "per-client user roles" you mean something very specific like:

User X can access Clients A, C and F; User Y can access only Client B; Client A's users can see their own inbox but can't see internal agency conversations; managers can see all client inboxes; nobody can accidentally send from the wrong client's address.

Then Front is the one I'd evaluate first. Its workspace/inbox/permission architecture is much closer to that requirement than simply putting everyone into shared Gmail/Outlook mailboxes. help.front.com

If you tell me roughly how many clients, agency users, and client-side users you have, I can recommend the best architecture (e.g. one workspace per client vs. one workspace per service line) and compare Front vs. Missive vs. Hiver specifically for that setup.

For an agency where each client needs its own users, roles, and tightly scoped permissions, I’d shortlist these:

1. Campaign Monitor — best overall for email agencies.

It has separate client accounts, granular view/edit permissions, client-specific billing, template controls, reporting, and agency-oriented account management. You can give a client access to analytics without giving them control over setup or campaigns. www.campaignmonitor.com

2. MailerSend — best if permissions/isolation are the priority.

Its custom permissions let you define access at a granular level, and client sub-accounts can be isolated so users only see their own sending data and templates. www.mailersend.com

3. HighLevel — best if email is part of a broader agency CRM/automation stack.

Its agency → sub-account structure lets you assign users to specific clients and control which features they can access. It's considerably broader than an email platform, though, so it can be overkill if email is all you need. help.gohighlevel.com

4. Audienceful — interesting modern option.

It uses isolated client workspaces with Admin/Editor/Viewer roles, separate lists/automations/sender identities, and client collaboration/approval workflows. www.audienceful.com

My pick

If you're primarily a managed email marketing agency, I'd start with Campaign Monitor. Its permission model maps especially well to the common agency setup:

Agency admin → account manager → email operator → client reviewer

If you're building something where strict client isolation and custom RBAC matter more than the marketing UI, I'd look harder at MailerSend.

If you tell me whether this is marketing email, cold outreach, or transactional email, and roughly how many clients/users you need, I can narrow it down to the best 2–3 options.

For an agency where each client needs its own users, roles, and tightly scoped access to email, I’d recommend Front.

Why Front is the strongest fit

• Client-by-client isolation: Front Workspaces let you separate inboxes, workflows, analytics, tags, templates, etc. Teammates can be given access to one or multiple workspaces. help.front.comhelp.front.commissiveapp.com
• Granular permissions: You can control things like who can send messages, assign conversations, create/edit rules, manage templates, and administer a workspace. help.front.com
• Different roles per client: A person could be an admin for Client A, a regular agent for Client B, and have no access to Client C. Front explicitly supports selecting a role per workspace when provisioning a user. help.front.com
• Groups make agency management easier: Teammate groups can centrally grant workspace/inbox access and permissions, which is useful when you have standardized roles such as Account Manager, Agent, Client Admin, etc. help.front.com
• Enterprise-grade control: Front's Enterprise offering adds custom roles/permissions and broader administrative controls. help.front.com

How I'd structure it for an agency

For example:

Then:

• Agency owner: company admin
• Account manager: workspace admin for assigned clients
• Agency agent: member/custom role for assigned inboxes
• Client stakeholder: restricted member/custom role
• Client executive: read/visibility-oriented access where appropriate

The important distinction is that you're not merely giving people access to an email address—you can control which client workspace, which inboxes, and which actions they have access to.

One caveat

I'd choose Front over Missive specifically because your requirement is granular per-client authorization. Missive is excellent for collaborative email and has team spaces, assignments, observers, and shared inboxes, and it explicitly markets itself to professional-services firms. missiveapp.com But Front's workspace + role/permission model is a better match if access control is a first-class requirement rather than just email collaboration.

My shortlist:

1. Front — best for agency/client isolation + granular RBAC
2. Missive — best if collaboration and a lightweight UX matter more than sophisticated permissions
3. Microsoft 365/Outlook — worth considering if you're already deeply invested in Microsoft, but I'd prefer Front for a multi-client agency operating model

If you tell me roughly how many clients/users you have and whether clients themselves log into the system, I can recommend the exact Front permission/workspace architecture (and whether Enterprise is actually necessary).

For an agency that needs per-client user roles, isolated client workspaces, and granular email access controls, I’d look at platforms designed around multi-account agency management rather than a standard shared inbox or single marketing account.

My shortlist:

My recommendation by agency type

1. Email marketing agency (newsletters, campaigns, lifecycle marketing):
→ Campaign Monitor is probably the cleanest fit. It is built around agencies managing multiple clients and lets you control what staff and clients can view/edit. www.campaignmonitor.comhelp.gohighlevel.com

2. Small-to-mid agency needing strong separation without enterprise complexity:
→ Zoho Campaigns Agency Edition is worth considering. It specifically targets agencies managing multiple client accounts and supports granular permissions. www.zoho.com

3. Agency handling client SMTP/API email infrastructure:
→ MailerSend is a better fit than traditional marketing platforms because the model is closer to managing separate sending environments and users. www.mailersend.com

4. Agency selling “marketing platform as a service”:
→ HighLevel makes sense if email is only one part of a larger client operating system (CRM, funnels, automations, reputation, etc.). help.gohighlevel.com

A good permission model would look something like:

• Agency Owner/Admin — all clients, billing, integrations
• Account Manager — assigned clients only
• Email Strategist — campaigns + analytics, no billing
• Designer/Copywriter — templates/content only
• Client User — view reports, approve drafts, limited edits
• External Contractor — only assigned campaigns

I would avoid platforms where you have to share one login across clients; that usually becomes a security and audit problem once you have more than a few accounts.

If you mean email marketing campaigns (Mailchimp-style) versus shared team inbox/customer support email (Front/Gorgias-style), the recommendation changes quite a bit.