ChatGPT answers, unedited

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 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.

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).