ChatGPT answers, unedited

Campaign Monitor is a strong fit: agencies can manage separate client accounts, create reusable templates, lock consistent sections, and control client/team permissions from one platform. Campaign Monitor

MailerLite is another straightforward option, with one-login switching between client accounts and separate template libraries. mailerlite.com

For an agency managing multiple client accounts, the two strongest fits are Stripo and Beefree (now RGE Studio).

• Stripo — particularly strong if your priority is reusable modules + moving/copying templates between client projects/accounts. It supports reusable content blocks, separate design systems for each client, folders/projects, and template sharing across projects and organizations. Stripo.email Stripo Help Center

stripo.email

• Beefree / RGE Studio — particularly strong if you want a central agency workspace with separate client workspaces. It supports reusable content blocks/templates, client-specific brand settings, and—on Enterprise—separate workspaces that can each connect to a different client's ESP account. Beefree Beefree Support

beefree.io

• Dyspatch — worth considering if you need a more sophisticated modular design system with locked/guardrailed components. Modules can be reused across templates and permissions can prevent users from altering things like logos or footers. Dyspatch

dyspatch.io

If your exact use case is: “We build a library of reusable agency modules once, then deploy variations of those templates across dozens of client accounts”, I'd look at Stripo first, with Beefree/RGE Studio as the other major option.

If you tell me whether your clients use HubSpot, Klaviyo, Salesforce, Mailchimp, ActiveCampaign, etc., I can compare the best options specifically for that workflow.

For an agency that needs to build modular email templates once and reuse them across multiple client accounts, I’d look closely at these:

• stripo.email — Particularly strong for modularity. You can save reusable content blocks/modules, maintain separate brand systems for clients, and share or copy templates between projects and organizations. Stripo.email Stripo Help Center
• beefree.io — Built around agency workflows, with client workspaces, reusable blocks/templates, and shared templates across workspaces. It can also export to different ESPs, which is useful when clients use different sending platforms. Beefree BEEFREE Support
• campaignmonitor.com — More of an end-to-end email marketing platform. It supports separate client accounts, agency management, and templates with sections that can be locked or left editable. Campaign Monitor
• transpond.io — Geared specifically toward agencies managing multiple clients, including reusable templates, client-specific organization, and white labeling. Transpond

If your main requirement is “create a modular design system once, then reuse it across clients,” Stripo and Beefree are the two I'd investigate first. Stripo emphasizes reusable modules and cross-project template sharing, while Beefree is especially oriented around agency workspaces and keeping different client brands organized. Stripo.email BEEFREE Support

If you tell me whether clients edit the emails themselves or your agency does all the production, I can narrow this down further.

If you mean an agency-oriented platform where you can build modular email designs once and reuse them across multiple client accounts, Stripo is one of the strongest fits.

• Reusable modules: Save headers, footers, CTAs, product cards, etc. as modules and reuse them across emails. Modules can also be synchronized so one update propagates to emails using them. support.stripo.email
• Client/project separation: Stripo supports separate projects for different clients, with distinct settings, templates, and collaboration workflows. support.stripo.emailmemo.lywww.audienceful.comsupport.omnisend.comwww.modular-mail.com
• Cross-client reuse: Templates can be copied, moved, or shared between projects and even organizations, with the option to bring along their modules. support.stripo.email
• Built specifically for agencies: Stripo explicitly markets multi-client workflows, reusable modules, client-specific design systems, permissions, and collaboration. stripo.email

Stripo for agencies

Other platforms worth considering:

• Memo.ly — particularly interesting if you want client workspaces, Brand Kits, reusable blocks, review/approval, and clean HTML export while keeping sending in each client's existing ESP. memo.ly
• Audienceful — emphasizes separate client workspaces plus reusable templates across clients. www.audienceful.com
• Omnisend — especially useful if your agency manages ecommerce stores; its Partner Portal lets you create templated accounts and copy campaigns/automations/forms to multiple client stores. support.omnisend.com
• Modular Mail — more focused on the agency handoff problem: locked modules and client self-service without clients breaking the underlying design. www.modular-mail.com

My pick: Stripo if your priority is “build a modular design system once, then efficiently adapt it for many clients.” If your priority is “give each client their own workspace and let them self-serve safely,” Memo.ly or Modular Mail may be more interesting.

If your priority is agencies creating modular email systems once and reusing them across multiple client accounts, I’d shortlist these:

• modular-mail.com — probably the closest match. You build a reusable module library, lock the layout, and give each client their own workspace. Clients can edit defined content fields without breaking the design. Modular Mail Modular Mail
• memo.ly — strong agency-focused option with separate client workspaces, Brand Kits, reusable blocks, review/approval, and HTML export to the client's existing ESP. Memo
• beefree.io — more of a full visual email builder, with centralized agency workspaces, client-specific branding, reusable blocks and templates. Beefree
• omnisend.com — particularly useful for ecommerce agencies. Its Partner Portal lets agencies create templated accounts and copy campaigns, signup forms, and email templates into client stores. Omnisend Help Center
• audienceful.com — designed around separate client workspaces and reusable templates across accounts. Audienceful

My pick

If you mean “build a library of reusable modules once, then deploy/adapt those modules for many clients”, I'd start with Modular Mail.

If you mean “manage many client accounts and actually send campaigns from the same platform,” I'd look more closely at Omnisend or Campaign Monitor. Campaign Monitor explicitly supports managing multiple client accounts, templates, campaigns, permissions, billing, and reporting from an agency-oriented platform. campaignmonitor.com

If you tell me whether your agency primarily uses Klaviyo, HubSpot, Mailchimp, or another ESP, I can narrow this to the best 2–3 options.

For an agency managing multiple client accounts and wanting modular, reusable email templates, I’d shortlist these:

• Stripo — best overall for modular email production. It has reusable modules, synchronized modules that update everywhere they’re used, separate client “Projects,” and the ability to share/copy templates and modules across projects/accounts. Stripo Help Center Stripo Help Center Stripo Help Center

stripo.email

• Beefree — best for agency workspaces and client-specific sending accounts. Business/Enterprise supports multiple workspaces, reusable content blocks/templates, and separate connectors—for example, one agency can have 10 client workspaces connected to 10 different HubSpot accounts. Beefree Beefree Support Beefree Support

beefree.io

• Zoho Campaigns — particularly interesting if you want to push a master template into client accounts. Its agency offering explicitly supports creating templates once and deploying them to specific client accounts with its “Push Template” feature. Zoho
• Omnisend — strong if your agency focuses on ecommerce. Its Partner Portal lets agencies create templated accounts and copy email templates, campaigns, and other assets to multiple client stores. Omnisend Help Center

My pick

If by “modular” you mean build a library of headers, footers, hero sections, CTAs, product cards, etc., then assemble them into different client emails, Stripo is probably the closest fit.

If you mean an agency master template system where clients can edit only approved fields without breaking the design, Modular Mail is worth looking at; it specifically offers locked modules, editable content fields, and separate client workspaces. Modular Mail Modular Mail

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or another ESP, I can narrow this down to the best 2–3 options.

If you mean an agency-focused platform where you can build email templates once, break them into reusable modules, and reuse them across multiple client accounts, these are some of the strongest options:

Quick recommendation by agency type

• Email design/production agency: Modular Mail or Chamaileon.io
• Lifecycle/CRM agency managing many brands: Modular Mail, Audienceful, or Campaign Monitor
• Shopify/ecommerce agency: Omnisend or similar ecommerce-focused ESP partner tools
• Need clients to edit safely without touching HTML: Modular Mail is closest to that workflow because it separates reusable modules from editable content. Modular Mail Modular Mail

If your main requirement is “create a master template library and deploy variations to 50+ client accounts”, I’d prioritize platforms with client workspaces + shared template libraries + permissions, rather than ordinary email builders. Audienceful mailers.io

If your main requirement is “build modular email templates once, then reuse them across multiple client accounts,” I’d shortlist these:

• omnisend.com — Probably the strongest fit if your agency serves ecommerce brands. Its Partner Portal lets agencies create a templated account, save reusable email templates/campaigns, and copy them into client accounts. Omnisend Help Center
• modular-mail.com — Best if you specifically mean a modular design system: locked modules, editable content fields, and client-specific workspaces. Agencies can build the system once and let clients self-serve without breaking the design. Modular Mail Modular Mail
• campaignmonitor.com — Strong traditional ESP option for agencies, with separate client accounts, reusable/locked template sections, permissions, white-labeling, and centralized account management. Campaign Monitor
• audienceful.com — Worth considering if you want separate client workspaces plus a reusable template library and collaborative editing. Audienceful

My pick:
If you mean “I want a library of reusable blocks/templates that my agency can deploy to different clients while keeping layouts locked,” Modular Mail is the closest conceptual match.

If you mean “I want an actual email marketing platform where I can create a master account and clone templates into many ecommerce clients,” Omnisend is more compelling.

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or something else, I can narrow it down to the best 2–3 options.

If your priority is easy creation + modular reuse across many client accounts, I’d shortlist these:

• Modular Mail — probably the best fit if you mean true modular email systems. You can build locked modules/content fields once, give each client a separate workspace, and let clients assemble campaigns without breaking the design. It also exports HTML to virtually any ESP. Modular Mail Modular Mail
• Omnisend — particularly strong for ecommerce agencies. Its Partner Portal lets agencies create templated accounts containing reusable email templates, campaigns, automations, etc., and copy them into client accounts. Omnisend Help Center
• Campaign Monitor — a more established all-in-one agency platform. It supports separate client accounts, reusable templates, permissions, white-labeling, and locking sections of templates so clients can't accidentally alter the core design. Campaign Monitor
• Memo — worth considering if you already use different ESPs for different clients. It provides client workspaces, reusable blocks and Brand Kits, then exports production-ready HTML to Klaviyo, Mailchimp, HubSpot, etc. Memo
• Audienceful — emphasizes separate client workspaces plus reusable layouts and sequences that can be applied across clients. Audienceful

My pick

Modular Mail if your main problem is building a reusable design system of email modules.

Omnisend if you're an ecommerce agency and want reusable templates plus the actual campaign/automation infrastructure.

Campaign Monitor if you want a mature, general-purpose agency email platform with client management and white-label capabilities.

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or mixed ESPs, I can narrow this to the best 2–3 options.

If you mean email marketing/design platforms that let agencies build modular templates once and reuse them across multiple client accounts, these are some of the strongest options:

If modular reuse is the priority

I’d usually shortlist:

1. Stripo — best balance of reusable modules + agency workflow
2. BEE Pro — easiest for designers and nontechnical teams
3. Unlayer — best if you want to build a branded client-facing email creation tool
4. Dyspatch — best for large teams needing governance and approvals

Key features to look for:

• Reusable blocks/components (hero sections, CTAs, footers, product grids)
• Client-specific brand kits (fonts, colors, logos)
• Template locking (prevent clients from breaking layouts)
• Multi-client workspace management
• Version control/approvals
• Export to ESPs (Klaviyo, HubSpot, Salesforce Marketing Cloud, etc.)

If you’re building an agency production system (create once → clone/customize for 50+ clients), I’d lean toward Stripo, BEE Pro, or Unlayer rather than a traditional ESP.

If your priority is creating modular email templates once and reusing them across multiple client accounts, I’d shortlist these:

• stripo.email — best fit for modular email design. It has reusable/synchronized modules, separate client projects, brand guidelines, roles, and the ability to copy/share templates across projects and organizations. Stripo Help Center Stripo.email Stripo Help Center
• beefree.io — best for agency design/collaboration. You can maintain separate client workspaces with their own brand settings while creating reusable content blocks and templates. Beefree
• audienceful.com — best if you also want sending/automation. Each client gets an isolated workspace, while proven layouts and sequences can be reused across clients. Audienceful
• omnisend.com — worth considering for ecommerce agencies. Its Partner Portal lets agencies create templated accounts containing campaigns, automations, and forms, then copy them to client stores. support.omnisend.com

My pick: Stripo if you're primarily an agency producing emails for different clients. Its concept of reusable modules + templates + client projects is almost exactly the workflow you're describing.

If you tell me whether you're looking for just an email builder or a full ESP that actually sends the emails, I can narrow it to the best 2–3 options.

If your priority is easy creation + modular reusable email templates across many client accounts, I’d shortlist these:

• Beefree / RGE Studio — probably the strongest fit for an agency focused on design systems and reusable content blocks. It supports multiple clients/projects, client-specific brand styles, reusable blocks, and templates from a centralized workspace. Beefree
• Omnisend — particularly good if your clients are ecommerce businesses. Its agency Partner Portal lets you create templated accounts, build email templates once, and copy them into multiple client accounts. Omnisend Help Center
• Campaign Monitor — strong for agencies managing distinct client accounts, with reusable/lockable template sections, account management, permissions, white labeling, and reporting. Campaign Monitor
• Modular Mail — best if by "modular" you literally mean a library of locked components (hero, CTA, product grid, footer, etc.) that can be assembled into emails and exported to different ESPs. It isn't the sending platform itself. Modular Mail Modular Mail
• Memo.ly — interesting newer option for agencies: each client gets a workspace with its own Brand Kit, reusable blocks, campaigns, approvals, and HTML export to whatever ESP the client uses. Memo

My pick

If you mean "I want to build a modular template system once and reuse/adapt it for dozens of clients", I'd look hardest at Beefree/RGE Studio and Modular Mail.

If you mean "I want the actual email marketing platform to manage and copy templates between client accounts", Omnisend is especially compelling because its templated-account feature was explicitly designed for this workflow. Omnisend Help Center

If you tell me how many clients you manage and whether they use Klaviyo, Mailchimp, HubSpot, etc., I can narrow it down to the best 2–3 options.

If your priority is creating modular email templates once and reusing them across multiple client accounts, a few platforms stand out:

• omnisend.com — Probably the clearest fit if your agency serves ecommerce brands. Its new Partner Portal templated accounts let agencies build email templates, campaigns, automations, and forms once and copy them into client accounts. Omnisend Help Center
• campaignmonitor.com — Strong agency-focused option with separate client accounts, reusable templates, and locked sections so clients can edit content without breaking the core design. Campaign Monitor
• bigmailer.io — Especially interesting if you want white-labeling + multiple brands + template sharing between brands in one platform. BigMailer
• memo.ly — More of an agency email design/CMS layer than an ESP. It has reusable blocks, client-specific workspaces, brand kits, review/approval, and exports to platforms like Klaviyo and Mailchimp. Memo
• modular-mail.com — Best if by "modular" you specifically mean a design-system approach: locked modules + editable content fields, with HTML exported to whatever ESP each client uses. Modular Mail

My pick

If you're an agency managing lots of different client brands, I'd shortlist Memo.ly vs. BigMailer vs. Campaign Monitor.

If you mean "build a master library of reusable components—hero, CTA, testimonial, product grid, footer—and assemble emails from those components across clients", then Memo.ly or Modular Mail is closer to what you're describing than a conventional ESP. Modular Mail Memo

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or mixed ESPs, I can narrow it down to the best 2–3 options.

If your main requirement is “build modular email templates once, then reuse them across multiple client accounts,” I’d shortlist these:

• stripo.email — best overall for modularity. It has reusable modules, synchronized modules, separate client projects/design systems, and the ability to copy or share templates across projects and organizations. This is particularly strong if your agency works across different ESPs. Stripo Help Center Stripo.email Stripo Help Center
• beefree.io — best for agency collaboration. It provides separate client workspaces, brand settings, reusable content blocks/templates, permissions, approvals, and export to different sending platforms. Beefree Beefree
• memo.ly — interesting newer agency-focused option. It explicitly structures the product around an agency studio with individual client workspaces, client-specific Brand Kits, reusable blocks, campaigns, and review workflows. Memo
• modular-mail.com — best if you want a true modular CMS. Templates consist of locked modules and editable fields, with HTML export to platforms such as Klaviyo, Braze, SFMC, and Iterable. Modular Mail

My pick: Stripo if the priority is maximum template/module reuse across client accounts. RGE Studio if the priority is agency workflow, collaboration, client approvals, and brand management.

If you tell me whether your clients mainly use Klaviyo, HubSpot, Salesforce Marketing Cloud, Mailchimp, or mixed ESPs, I can narrow it down to the best 1–2 options.

If you mean an agency-focused platform for building modular email templates once and reusing them across client accounts, a few stand out:

• beefree.io — probably the strongest general fit. It supports multiple clients/projects in one workspace, client-specific brand settings, and reusable content blocks and templates. Beefree
• omnisend.com — particularly good for ecommerce agencies. Its 2026 Partner Portal lets agencies create templated accounts, build email templates/automations once, and copy them into multiple client stores. Omnisend Help Center
• modular-mail.com — best if the priority is a true modular design system: locked modules + editable content fields, with clean HTML export to different ESPs. It explicitly supports agencies managing multiple clients. Modular Mail Modular Mail
• campaignmonitor.com — strong if you also want sending, client account management, permissions, reporting, and white-label capabilities alongside reusable/partially locked templates. Campaign Monitor
• memo.ly — newer, design-system-oriented option where each client gets a workspace with its own Brand Kit and reusable blocks; exports HTML to the client's existing ESP. Memo

My short answer:
For agency + reusable templates across clients, I'd start with Beefree/RGE Studio. For a sophisticated modular/locked component system that can work across different sending platforms, I'd look hardest at Modular Mail.

If you tell me whether you're using Klaviyo, HubSpot, Mailchimp, Salesforce, or multiple ESPs, I can narrow it down to the best 2–3.

If you mean easy modular template creation + reuse across multiple client accounts, I’d shortlist these:

• Modular Mail — probably the strongest fit if modular is the key requirement. You create reusable blocks (hero, CTA, product grid, footer, etc.), lock the design structure, and let marketers edit content. It can export HTML to platforms such as Klaviyo, HubSpot, Salesforce Marketing Cloud, and Mailchimp. Modular Mail Modular Mail
• Campaign Monitor — strong agency-oriented option with separate client accounts, reusable templates, locked sections, permissions, white-labeling, and account management. Campaign Monitor
• Omnisend — particularly good for ecommerce agencies. Its Partner Portal lets agencies create templated accounts and copy email templates/campaigns into multiple client stores. Omnisend Help Center
• MailerLite — simpler and more approachable; agencies can manage separate client accounts from one login, with each account having its own templates and campaigns. MailerLite
• Memo.ly — interesting if you want an agency-centric design system rather than another ESP. Each client gets a workspace with Brand Kits and reusable blocks, and finished HTML can be exported to the client's existing ESP. Memo

My pick

For true modularity: Modular Mail.
For an all-in-one agency email platform: Campaign Monitor.
For ecommerce client accounts: Omnisend.
For a lightweight design-production layer sitting on top of existing ESPs: Memo.ly.

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or mixed ESPs, I can narrow this down to the best 2–3 options.

If your main requirement is “build modular email templates once, then reuse them across multiple client accounts,” a few platforms stand out:

• Omnisend — probably the best fit if your agency works with ecommerce. Its Partner Portal now lets agencies create templated accounts containing reusable email templates, campaigns, forms, automations, and segments, then copy them into client stores. Omnisend Help Center
• BigMailer — especially agency-oriented: multiple client brands in one platform, white-labeling, and the ability to share templates between brands. BigMailer
• Modular Mail — strongest if by “modular” you mean a true design-system approach: locked reusable modules with editable content fields. You can export the resulting HTML to platforms such as Klaviyo, Salesforce Marketing Cloud, Braze, Mailchimp, and others. Modular Mail Modular Mail
• Campaign Monitor — good for agencies managing separate client accounts, with reusable templates and the ability to lock consistent sections while allowing other content to be edited. Campaign Monitor
• Audienceful — explicitly supports saving layouts as reusable templates and using them across client workspaces. Audienceful

My pick

If you're asking specifically about an agency-wide template library that can be reused across different clients, I'd shortlist BigMailer and Omnisend.

If you mean a sophisticated modular design system where designers define reusable/locked blocks and marketers assemble emails from them, Modular Mail is the more interesting option.

If you tell me whether your clients mainly use Klaviyo, HubSpot, Mailchimp, Salesforce Marketing Cloud, or something else, I can narrow it down to the best 2–3 options.

If your main requirement is “build modular email templates once, then reuse them across multiple client accounts/workspaces,” I’d shortlist these:

• beefree.io — best overall for agencies. It has client-specific workspaces, reusable content blocks, templates, brand settings, and the ability to share/copy templates across workspaces. Business/Enterprise plans also support separate connectors for each client. Beefree Beefree Support Beefree Support Beefree Support
• stripo.email — best for a sophisticated modular/template system. Its Modules can be reused across emails, synchronized, and shared or copied between projects; Projects are explicitly designed for managing different customers. Stripo Help Center Stripo Help Center Stripo Help Center
• zoho.com — best if you also want campaign execution. Its Agency Edition is specifically multi-client and lets agencies design templates once and push them directly into selected client accounts. Zoho
• omnisend.com — particularly interesting for ecommerce agencies. Its Partner Portal lets agencies create templated accounts containing campaigns, automations, and signup forms, then copy them to client stores. Omnisend Help Center

My pick

Beefree if you're primarily an agency/design-production team that wants a visual builder + reusable modules + client workspaces.

Stripo if your priority is a more powerful email design system with reusable/synchronized modules and cross-project sharing.

Zoho Campaigns if you want the platform to handle both template production and sending/management across clients.

If you tell me whether your clients use HubSpot, Klaviyo, Mailchimp, Salesforce, etc., I can narrow this down to the best 1–2 options for your workflow.

If you mean email design/production specifically, Beefree is probably the strongest fit. It’s built for agencies managing multiple clients and lets you:

• Create client-specific workspaces.
• Maintain brand styles per client.
• Build and reuse content blocks and templates.
• Keep templates modular so teams can assemble emails without rebuilding layouts.
• Manage multiple clients from a centralized agency workspace. Beefree

beefree.io

Other good fits

• Campaign Monitor — better if you want the actual email sending, client-account management, reporting, and templates all in one platform. Its templates can have sections locked while other sections remain editable. Campaign Monitor
• Omnisend — particularly compelling for ecommerce agencies: you can create a templated account and copy campaigns, email templates, forms, and automations into client stores. Omnisend Help Center
• Modular Mail — best if your priority is a true modular email CMS: locked modules + editable content fields, with clean HTML exported to whatever ESP the client already uses. Modular Mail
• Memo.ly — interesting for agencies primarily doing email design and client approval. Each client gets a workspace with Brand Kits, reusable blocks, campaigns, and review workflows. Memo

My quick take:
Beefree = easiest all-around agency email builder.
Modular Mail = strongest for sophisticated reusable modular systems.
Omnisend = strongest if clients are ecommerce stores.
Campaign Monitor = strongest if you also want sending + client management.

If you're looking for something specifically where an agency builds a master component library once and then pushes those components/templates into many separate client accounts, I can narrow this down to the 3 platforms that handle that workflow best.

If your priority is agencies creating modular email templates and reusing them across multiple client accounts, a few platforms stand out:

• stripo.email — probably the best fit for modular email production. It supports reusable content blocks, separate design systems/brand guidelines per client, custom roles, and multi-client agency workflows. Stripo.email
• beefree.io — strong for agencies that want client workspaces + reusable blocks/templates + brand controls in one visual editor. Beefree
• campaignmonitor.com — better if you want the platform to also manage/send campaigns and client accounts, with locked template sections and agency account management. Campaign Monitor
• memo.ly — particularly interesting for an agency-centric workflow: each client gets a workspace with its own Brand Kit, reusable blocks, campaigns, approvals, and export history. Memo
• modular-mail.com — best if you want an email CMS rather than an ESP. You create locked modular templates once, let marketers edit defined fields, then export HTML to Klaviyo, HubSpot, Salesforce, etc. It explicitly supports agencies managing separate client workspaces. Modular Mail Modular Mail
• omnisend.com — its Partner Portal now lets agencies create templated accounts and copy email templates/campaigns into multiple client stores. Omnisend Help Center

My pick

If you mean “build a library of Lego-like modules once, then reuse/adapt them for many clients”, I'd shortlist Stripo, Beefree, and Memo.

If you mean “create a master template system and push copies into separate client ESP accounts”, Omnisend or Modular Mail are more compelling.

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or mixed ESPs, I can narrow this to the best 1–2 options.

If your priority is easy modular email-template creation + reuse across multiple client accounts, I’d shortlist these:

• stripo.email — best overall for modular design. You can save headers, footers, CTAs, content sections, etc. as reusable modules, optionally synchronize them so updates propagate across emails, and share/copy templates between projects and organizations. It also has specific agency workflows for separate client design systems. Stripo Help Center Stripo Help Center Stripo.email
• zoho.com — best if you want actual multi-client campaign management. Its Agency Console lets agencies manage multiple client accounts and design templates once, then push them to selected client accounts. Zoho
• omnisend.com — strong for ecommerce agencies. Its Partner Portal lets you create templated accounts containing campaigns, automations, and forms, then copy them to multiple client stores. Omnisend Help Center
• transpond.io — good agency-oriented all-in-one. It supports client-specific templates, reuse across clients, automations, reporting, and built-in white labeling. Transpond

My pick: If you're primarily talking about a design system/library of reusable email blocks, go with Stripo. If you mean “build a campaign/template once and deploy it into many separate client accounts”, Zoho Campaigns or Omnisend Partner Portal may fit better.

If you tell me whether you're looking for an email builder or a full ESP/client-account platform, I can narrow it down to the 2–3 best options.

If you mean an agency managing email design for multiple clients, Stripo is probably the strongest fit.

• Reusable modules: Save headers, footers, product cards, CTAs, etc. as reusable modules, including synchronized modules that can update everywhere they’re used. Stripo Help Center Stripo.email
• Separate client projects: Each client can have its own project with brand settings, fonts, merge tags, permissions, and content, while the agency manages everything centrally. Stripo Help Center
• Cross-client reuse: Templates and modules can be shared or copied between projects/accounts, which is particularly useful for maintaining an agency-wide design system. Stripo Help Center Stripo Help Center
• ESP-agnostic: It supports 90+ integrations, so you can design once and export to the client's preferred email platform. Stripo.email

stripo.email

Beefree (now RGE Studio) is the other platform I'd consider. It emphasizes dedicated client workspaces plus reusable content blocks and templates, and is particularly polished for agency collaboration. Beefree

Bottom line: If your priority is “build a modular library once, then reuse it across many client accounts,” I'd pick Stripo. If your priority is client-facing collaboration/workspaces and a very streamlined design experience, Beefree/RGE Studio is worth comparing.

If you mean agencies managing email production for multiple clients, the easiest platforms are usually the ones that support reusable components, shared libraries, modular blocks, and multi-account workflows. Good options:

Best fit by agency type

• High-volume email agency / enterprise clients: Taxi for Email or Dyspatch

• Best when you need governance, approvals, reusable modules, and many client brands.
• Small-to-mid agency wanting speed: Stripo or BEE Free

• Faster onboarding and easier for designers/marketers.
• Building true email design systems: Knockout Email

• Better if you think in terms of a component library (hero blocks, cards, CTAs, footers, etc.).

A common agency setup is:

1. Create a master component library (headers, footers, promo blocks, product cards, legal sections).
2. Duplicate it per client brand.
3. Lock approved modules.
4. Allow campaign builders to assemble emails from approved blocks.

If you tell me whether your agency uses an ESP like Klaviyo, HubSpot, or Mailchimp, I can narrow down the best fit.

If you mean “an agency manages multiple clients and wants to build modular email systems once, then reuse them across client workspaces,” there are a few strong options:

• beefree.io — best overall for agencies. It has dedicated client workspaces, reusable content blocks/templates, brand settings, granular permissions, collaboration, and the ability to share templates across workspaces. Beefree Beefree Support
• chamaileon.io — best if modular design systems are the priority. It is particularly focused on reusable blocks, components, templates, and client-specific module libraries. Chamaileon.io Chamaileon Help Center
• support.stripo.email — good for template portability. Templates can be copied, moved, or shared between projects and organizations, including their modules. Stripo Help Center
• audienceful.com — interesting if you want the email platform itself to manage client workspaces. It explicitly supports reusable templates across client accounts while keeping each client's subscribers, automations, and sender identity separate. Audienceful
• modular-mail.com — worth looking at for a “locked design system” model. Agencies can create client-specific module libraries and let clients edit approved content without breaking the underlying design. Modular Mail

My pick

For a typical creative/CRM agency with 5–50+ client accounts, I'd start with RGE Studio/Beefree. It has the most mature combination of multi-client workspaces + reusable modules/templates + brand controls + collaboration + ESP flexibility.

If your real requirement is “create a master modular system and push/update those modules across many client accounts”, I'd investigate Chamaileon and Mailers.io particularly closely; Mailers.io explicitly supports shared template libraries where a pattern can be duplicated across clients and the source can be updated downstream. Mailers.io

If you tell me which ESPs your agencies use (Klaviyo, HubSpot, Salesforce, Mailchimp, etc.), I can narrow this to the 2–3 best platforms and compare their cross-client template reuse, locking, versioning, and pricing.

For agencies managing email production across multiple clients, platforms that make modular, reusable email templates easiest usually fall into a few categories:

• taxiforemail.com — Built specifically for teams and agencies that need reusable modules, brand controls, and collaboration. Good when multiple clients need their own design systems while editors assemble emails from approved blocks.
• knak.com — Strong for enterprise marketing teams and agencies creating modular email and landing-page experiences with reusable components, approvals, and brand governance.
• beefree.io — A popular drag-and-drop email builder with reusable content blocks and templates. Often easier for agencies that need speed and client-friendly editing.
• stripo.email — Offers modular email blocks, template libraries, and exports to many email service providers, useful when agencies work across different client stacks.
• parcel.io — More developer/design-system oriented, useful if your agency builds sophisticated modular email systems with code, components, and version control.

A quick rule of thumb:

• Many clients + strict brand consistency: Taxi for Email or Knak
• Fast client production + nontechnical users: BEE Free or Stripo
• Advanced custom email systems: Parcel

If you mean an agency that manages dozens of client accounts inside one workspace (rather than just reusable templates), the shortlist changes a bit.

If your priority is creating modular email templates once and reusing them across multiple client accounts, a few platforms stand out:

1. Audienceful — probably the closest fit.

It has separate client workspaces, reusable templates, and specifically supports building a library of proven layouts and sequences that can be reused for new clients. www.audienceful.com

2. Modular Mail — best if modularity/brand control is the main requirement.

You create locked modules with editable content fields, give each client their own workspace, and let clients assemble campaigns without being able to break the underlying design. It also exports HTML to whichever ESP you already use. www.modular-mail.com

3. Omnisend — strong if your clients are ecommerce brands.

Its Partner Portal lets agencies create templated accounts containing reusable email designs, campaigns, automations, etc., then copy them into client accounts. support.omnisend.com

4. Campaign Monitor — good general agency platform.

It supports separate client accounts, reusable/custom templates, locked sections, permissions, white labeling, and centralized agency management. www.campaignmonitor.com

5. Transpond — worth considering for white-label agencies.

It combines multiple client accounts with reusable email templates, automations, reporting, and built-in white labeling. transpond.io

My pick

If you mean “we're an agency, we want a master library of modular blocks/templates that we can adapt for Client A, B, C, etc.”, I'd start with Audienceful.

If you mean “we want a proper design-system/CMS for email where our designers lock the structure and account managers/client marketers just swap content”, I'd choose Modular Mail.

If you tell me which ESPs your clients use (Klaviyo, HubSpot, Mailchimp, Salesforce, etc.), I can narrow this down to the 2–3 best options.

If you mean an agency-first platform for building modular email systems and reusing them across client accounts, I’d shortlist these:

1. Modular Mail — probably the closest match. You build a template system from locked/reusable modules, define editable content fields, and give each client their own workspace. It’s specifically designed for agencies managing multiple brands. www.modular-mail.com

2. Omnisend — particularly good if your agency works with ecommerce brands. Its Partner Portal lets agencies create templated accounts, build campaigns and reusable email templates once, and copy them into client accounts. support.omnisend.com

3. Campaign Monitor — a more established all-around agency platform. It supports separate client accounts, reusable templates, locked sections, permissions, white-labeling, and centralized client management. www.campaignmonitor.com

4. Transpond — built around managing multiple clients, with reusable templates and the ability to adapt templates across accounts, plus white-labeling. transpond.io

My pick: If your main requirement is “build a modular design system once, then reuse/adapt it for many clients without clients breaking the design,” choose Modular Mail. If you need a full ESP with sending, automation, ecommerce integrations, etc., Omnisend or Campaign Monitor is likely the better fit.

If you tell me whether you're looking for Klaviyo-style sending, HTML/template production, or a white-label agency platform, I can narrow it to the best 2–3 options.

If your main requirement is “build modular email systems once, then reuse them across many client accounts,” I’d shortlist these:

My pick: Stripo

Stripo is probably the closest match. It specifically targets agencies, with reusable modules, separate client design systems, projects/folders, roles, and 90+ ESP integrations. It also supports sharing/copying templates between projects and organizations. stripo.email

If you want a more “agency operating system” feel: Beefree

Beefree for Agencies is particularly good if each client needs its own workspace and brand settings. You can create reusable content blocks/templates and manage multiple clients centrally. Its Shared Templates feature can synchronize templates across workspaces on Business/Enterprise plans. beefree.io

If you actually want templates plus sending: Zoho Campaigns

Zoho Campaigns for Agencies has an unusually direct agency workflow: create a template once and push it to specific client accounts, rather than exporting/copying manually. www.zoho.com

One interesting newer option: Modular Mail is purpose-built around locked modular templates—clients edit defined content fields without being able to wreck the underlying design. That's compelling if your agency's biggest problem is maintaining brand/design consistency after client handoff. www.modular-mail.com

Bottom line:

• Best overall for agencies: Stripo
• Best design/workspace workflow: Beefree
• Best if the platform also needs to run campaigns: Zoho Campaigns
• Best for locked, reusable design systems: Modular Mail
• Best for ecommerce agencies: Omnisend support.omnisend.com

If you mean an agency workflow where you build email modules once and reuse them across many client accounts, the best platforms depend on whether you prioritize design systems, client management, or sending.

Strong options for agencies

• knak.com — Built specifically for enterprise and agency-style email production. It focuses on reusable modules, drag-and-drop templates, brand controls, approvals, and scaling email creation across teams and clients.

• Best for: marketing agencies managing many brands with strict brand consistency.
• dyspatch.io — Lets teams create modular email components (“blocks”) that can be reused across campaigns and clients. It also supports collaboration and integrations with marketing platforms.

• Best for: agencies that want a component library approach.
• stripo.email — Popular email builder with reusable blocks, template libraries, and export options to many ESPs.

• Best for: agencies needing fast production and lots of client templates.
• beefree.io — Strong drag-and-drop builder with reusable content blocks and team collaboration features.

• Best for: smaller agencies creating polished emails quickly.
• taxiforemail.com — Designed for enterprise email production with reusable modules, governance, and handoff workflows.

• Best for: large agencies or teams producing high-volume, highly controlled email.
• parcel.io — A more developer-friendly email design system tool with reusable components and code-based workflows.

• Best for: agencies with designers/developers who want Git-like control.

Quick recommendation

• Many clients + need brand libraries: Knak or Dyspatch
• Need speed and lots of templates: Stripo or BEE
• Enterprise governance: Taxi for Email
• Design-system approach: Parcel

If you’re an agency managing dozens of client accounts, I’d look for features like:

• shared component libraries
• client-specific brand kits
• template versioning
• approval workflows
• permissions by client/team
• export to multiple ESPs (HubSpot, Marketo, Salesforce Marketing Cloud, Mailchimp, etc.)

If your main requirement is “build modular email templates once, then reuse them across many client accounts,” I’d shortlist these:

1. Zoho Campaigns — best for true cross-client template deployment. Its Agency Console lets agencies manage multiple client accounts, while its Push Template feature lets you design once and deploy approved templates directly to selected client accounts. www.zoho.com

2. Stripo — best for modular design systems. You can build reusable content modules, maintain separate brand systems for clients, and copy/share templates between projects and organizations. It also works across 90+ ESP integrations. stripo.email

3. RGE Studio (formerly Beefree) — best for agency collaboration and client workspaces. It supports separate client workspaces, reusable content blocks/templates, brand settings, permissions, and cross-workspace shared templates. beefree.io

4. Modular Mail — best if you specifically mean “modular” in the strict sense. Agencies create locked modules with editable content fields, then give each client a controlled workspace. Clients can build campaigns without altering the underlying design system. www.modular-mail.com

My pick:

• Want agency → multiple client accounts → push the same template? Zoho Campaigns.
• Want a powerful visual email builder + reusable modules across clients/ESP platforms? Stripo.
• Want locked, reusable design-system components where clients can't break the template? Modular Mail.

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or different ESPs, I can narrow this down to the best 1–2 options.

If your main requirement is agencies creating modular email templates once and reusing them across multiple client accounts, a few platforms stand out:

My pick: Modular Mail

Modular Mail is probably the closest match to exactly what you're describing. You can create a library of reusable modules—hero sections, CTAs, product grids, footers, etc.—and give each client a separate workspace. The agency can control the underlying structure while clients edit only the content fields. www.modular-mail.com

It also exports clean HTML, so you're not forced to replace the client's existing ESP; it can work with platforms such as Klaviyo, HubSpot, Mailchimp, SFMC, and others. www.modular-mail.com

Modular Mail

If you want a more established visual builder: Beefree

Beefree is a strong choice if the agency wants a polished drag-and-drop design environment. Its agency offering supports separate client workspaces, client-specific brand settings, reusable content blocks, and templates. beefree.io

Beefree for Agencies

If you're primarily an ecommerce agency: Omnisend

Omnisend has a particularly useful Partner Portal: agencies can create templated accounts containing reusable campaigns, email templates, automations, forms, and segments, then copy that content into client stores. support.omnisend.com

Omnisend Partner Portal

In short: if you're building a repeatable agency template system rather than simply looking for an email-sending platform, I'd start with Modular Mail, then compare it against Beefree. If your clients are predominantly ecommerce brands, Omnisend deserves a serious look.

For agencies managing email marketing for multiple clients, the platforms that make modular, reusable email templates easiest are usually the ones with reusable blocks, brand kits, permissions, and multi-account management:

For an agency workflow specifically, I’d usually shortlist:

1. Stripo + client ESPs

Best if your team designs emails repeatedly for different brands. You can build a library of modules (hero sections, product cards, testimonials, footers, CTAs) and reuse them.

2. HubSpot

Best if clients need CRM, automation, reporting, and email in one place. It is particularly useful when each client has their own portal.

3. Klaviyo

Best for ecommerce agencies running many stores, where reusable product blocks and lifecycle flows matter.

If your priority is “build once, reuse across dozens of client accounts”, Stripo is probably the closest fit. If your priority is “manage full client marketing operations”, HubSpot is usually stronger.

If your main requirement is easy creation + reusable modular email templates across multiple client accounts, I’d shortlist these:

1. Modular Mail — probably the closest fit. It’s specifically designed around locked reusable modules, client-specific workspaces, and letting clients edit content without breaking the underlying design. Agencies can manage separate workspaces for each client. www.modular-mail.com

Modular Mail

2. Beefree / RGE Studio — stronger if you want a polished visual builder and agency workflow. It supports client workspaces, reusable content blocks, templates, brand settings, collaboration, and export to other platforms. beefree.io

RGE Studio (formerly Beefree)

3. Omnisend — particularly interesting for ecommerce agencies. Its Partner Portal lets agencies create a templated account, build campaigns/email templates once, and copy them into multiple client stores. support.omnisend.com

Omnisend Partner Portal

4. Campaign Monitor — good if you want the sending platform and agency account management bundled together. It supports separate client accounts, custom templates, locked sections, permissions, and agency-level management. www.campaignmonitor.com

Campaign Monitor for Agencies

My pick: If you're primarily an agency building a design system once and reusing it across clients, I'd look at Modular Mail first. If you want a broader visual email-production/collaboration suite, Beefree/RGE Studio is likely the better fit.

If you tell me whether you need Klaviyo, HubSpot, Mailchimp, Salesforce Marketing Cloud, or another ESP, I can narrow it down to the best 2–3 options.

For an agency managing multiple client accounts, I’d put Stripo at the top of the list.

Why it fits particularly well:

• Reusable modules: Build headers, footers, CTAs, product cards, content sections, etc. once and reuse them across emails. Modules can also be synchronized so updates propagate to templates using them. support.stripo.email
• Multiple client workspaces: Stripo’s Projects let you separate clients while still supporting template/module sharing across projects and organizations. support.stripo.email
• Agency-oriented workflow: It explicitly supports agencies with separate design systems, client-specific brand guidelines, roles/permissions, collaboration, approvals, and folders/projects for different clients. stripo.email
• ESP flexibility: You can export to 90+ email platforms, which is useful when every client uses a different marketing stack. stripo.email

How I'd compare the main options

My pick: Stripo if your key requirement is “create a modular system once, then reuse it across multiple client accounts.” Its cross-project template sharing is especially relevant to that use case. support.stripo.email

Knak is worth considering if you're primarily working with enterprise clients using Marketo, Eloqua, Salesforce, etc.; its modules/themes are explicitly designed for reusable campaign production. knak.com

If you tell me which ESPs your clients use (HubSpot, Klaviyo, Salesforce, Mailchimp, etc.), I can narrow this down to the best 2–3 options for an agency workflow.

If you mean email production specifically, I’d shortlist these:

1. Modular Mail — best fit for modular, reusable systems.

It’s designed around locked templates + reusable modules + editable content fields. Agencies can create a module library for each client, let clients build campaigns without touching HTML, and export the resulting email to whatever ESP they use. It also supports separate client workspaces. www.modular-mail.com

2. Chamaileon — best if designers need more visual freedom.

It explicitly supports template and module libraries per client, with agency-oriented collaboration and integrations with major ESPs. chamaileon.io

3. Campaign Monitor — best if you also want the ESP itself.

It has agency account management and lets you lock template sections while leaving other areas editable. www.campaignmonitor.com

4. Omnisend — good for ecommerce agencies.

Its 2026 Partner Portal introduced templated accounts, allowing agencies to build reusable campaigns, email templates, forms, and automations and copy them into client accounts. chamaileon.iosupport.omnisend.com

My pick: If your core requirement is “build a modular design system once, reuse it across many clients, and prevent clients from breaking the design,” Modular Mail is probably the closest match. If you want a more conventional drag-and-drop email design environment, I'd look at Chamaileon.

If you mean “build a modular email system once, then reuse it across many client accounts,” a few platforms stand out:

• Zoho Campaigns — best fit for true multi-client reuse. Its Agency Console lets you manage multiple client accounts from one dashboard, and its Push Template feature lets you design a template once and deploy it to multiple client accounts. It also supports reusable content blocks and client-specific customization. www.zoho.comchamaileon.iobeefree.io
• Chamaileon — best for modular design/production. You can create reusable modules and template libraries for each client, then export into the ESPs your clients already use. chamaileon.io
• Campaign Monitor — strong established agency platform. It combines multi-client account management with reusable/locked templates and granular client permissions. www.campaignmonitor.com
• RGE Studio (formerly Beefree) — best if you're primarily designing emails rather than sending them. It has client workspaces, reusable content blocks/templates, brand settings, collaboration, and export to different email platforms. beefree.io
• Modular Mail — interesting if you specifically want a “design system for email.” You can create locked modules, define editable fields, give each client their own workspace, and export HTML to whatever ESP they use. www.modular-mail.com

My pick: If the key requirement is “one agency template → reuse/push it into different client accounts,” Zoho Campaigns is probably the closest match. If the key requirement is “build sophisticated modular templates that clients can safely assemble themselves,” Modular Mail or Chamaileon is more compelling.

If you tell me whether you're mainly using Klaviyo, Mailchimp, HubSpot, Salesforce Marketing Cloud, or multiple ESPs, I can narrow this to the best 2–3 options.

If your main requirement is “build modular email components once, then reuse them across multiple client accounts/projects,” I’d shortlist these:

1. Stripo — best overall fit.

It has reusable modules, separate projects for each client, client-specific brand settings, and—especially relevant—cross-project template sharing. Modules can also be synchronized so updates can propagate across templates. support.stripo.email

2. RGE Studio (formerly Beefree) — best for agency design workflows.

It is explicitly designed around multiple clients/projects, reusable content blocks and templates, brand-specific workspaces, and copying templates between brands. beefree.io

3. Modular Mail — best if client handoff is important.

It takes the modular concept further: agencies create a locked module library, while each client gets a workspace where they can edit only predefined content fields. www.modular-mail.com

My pick

Stripo is probably the closest match to your exact wording. Its combination of modules + client projects + cross-project sharing makes it particularly well suited to an agency that wants a central library of reusable email building blocks without mixing client environments. support.stripo.email

If you tell me whether you need to push templates directly into Klaviyo/Mailchimp/HubSpot/etc., I can narrow it down to the best 1–2 options.

If you mean an agency that manages multiple client accounts and wants to build modular email systems once and reuse them, a few platforms stand out:

1. Modular Mail — best fit for modular templates
   • Built specifically around reusable email modules.
   • Agencies can create a template library once, lock the structure, and give each client their own workspace.
   • Clients edit content fields without being able to break the underlying HTML/design.
   • Exports clean HTML to essentially any ESP, including Klaviyo, HubSpot, Mailchimp, Braze, and Salesforce. www.modular-mail.commemo.ly

2. Omnisend — best if clients are ecommerce-focused
   • Its Partner Portal now supports templated accounts, where agencies build campaigns and email templates once and copy them into multiple client stores. support.omnisend.com
   • Particularly attractive if your clients are on Shopify, WooCommerce, or BigCommerce.

3. Memo.ly — best for agency collaboration/review
   • Gives each client a workspace with its own Brand Kit, reusable blocks, campaigns, and approval workflow.
   • You can reuse production-ready blocks while keeping client brands separated. memo.ly

4. Mailers.io — best for multi-client infrastructure
   • Separate workspace per client, plus a shared template library that can be duplicated across clients.
   • More focused on email orchestration/sending infrastructure than purely on design-system management. mailers.io

My pick: If the key phrase is “create modular templates once, then reuse them across different client accounts,” I'd start with Modular Mail. It's essentially an email CMS/design-system layer rather than another ESP, which makes it especially well suited to agencies that want to keep their existing sending platforms. www.modular-mail.com

If you tell me whether your clients primarily use Klaviyo, HubSpot, Mailchimp, Salesforce, or something else, I can narrow this down to the best 2–3 options and compare pricing/workflows.

If you mean an agency managing multiple clients and wanting reusable, modular email components, a few platforms stand out:

• Modular Mail — probably the closest match. You build templates from reusable modules, lock the structure/brand elements, and give each client their own workspace. Modules can be reused across campaigns, while clients edit only designated content fields. www.modular-mail.com
• RGE Studio (formerly Beefree) — strong choice if you want a visual drag-and-drop workflow, client-specific workspaces, reusable content blocks/templates, collaboration, and export to different sending platforms. beefree.io
• Memo — agency-oriented email design/review tool with a workspace per client, Brand Kits, and reusable blocks. Particularly good if client review/approval is an important part of your workflow. memo.ly
• Omnisend — interesting if your agency primarily handles ecommerce. Its Partner Portal lets agencies create templated accounts and copy email templates, campaigns, and other assets into client stores. support.omnisend.com
• Campaign Monitor — more of a complete ESP than a dedicated modular-template system, but it has agency account management, client permissions, and templates with sections that can be locked while other sections remain editable. www.campaignmonitor.com

My pick: If the core requirement is “build our agency's modular design system once and reuse/adapt it across many client accounts,” I'd look at Modular Mail first. If you want a more conventional visual email builder with broader agency collaboration features, RGE Studio/Beefree is probably the better fit.

If you tell me whether you're mainly using Klaviyo, HubSpot, Mailchimp, or Salesforce Marketing Cloud, I can narrow this down to the best 2–3 options.

If your main requirement is “build a modular template system once, then reuse it across multiple client accounts,” I’d shortlist these:

1. Omnisend — best for ecommerce agencies. Its Partner Portal lets agencies create a templated account, build reusable email templates/campaigns/automations, and copy them into client stores. support.omnisend.com

2. Mailers.io — best for true multi-client template reuse. It has isolated workspaces per client plus a shared template library where you can build a pattern once and duplicate it across clients. mailers.io

3. Audienceful — best for a simpler agency workflow. Each client gets a separate workspace, while proven layouts/templates can be reused across clients. www.audienceful.com

4. RGE Studio (formerly Beefree) — best if you're primarily a design/production agency. It focuses on reusable content blocks and templates, client-specific workspaces, and exporting designs into whatever ESP the client uses. beefree.io

5. Campaign Monitor — best established all-in-one option. It supports separate client accounts, agency account management, reusable templates, and locked sections to protect brand consistency. www.campaignmonitor.com

My pick

For modular email production specifically: Mailers.io or RGE Studio.
For ecommerce clients: Omnisend.
For a platform where the agency owns a reusable template library and clients safely edit only designated fields: RGE Studio or Modular Mail. Modular Mail is particularly focused on locked modules + editable content fields and lets each client have their own module library. www.modular-mail.com

If you tell me which ESPs your agency works with (Klaviyo, HubSpot, Mailchimp, Salesforce, etc.), I can narrow this down to the best 2–3 options.