Best / Email marketing
Best open-source Email marketing
The best open-source email marketing tools in the c17.io catalog are Plunk for broadcasts and transactional mail, posta as a self-hosted Mailgun/SendGrid-shaped relay, FluentCRM if the site is already WordPress, and Mailflare when the job is domain email plus a booking page. listmonk is the published Substack/ConvertKit stack but is not a Crew catalog row, so it is linked via /stacks/listmonk-email rather than ranked here.
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Ranked picks
1
Plunk EmailOpen-source email platform on the c17 Mailchimp/SendGrid/Postmark stack.
When to pick it: Lists and transactional mail you host.
2
postaAGPL HTTP-to-SMTP relay positioned as a Mailgun/SendGrid alternative.
When to pick it: Sending mail you already composed, not a visual campaign builder.
526 stars in the catalog
3
FluentCRMWordPress marketing automation plugin for leads and segments.
When to pick it: A WP site that wants CRM-ish campaigns without a new SaaS.
4
mailflareAGPL email, calendar, and booking on Cloudflare Workers — the c17 office stack.
When to pick it: Apex mail and a booking page, not a Klaviyo-style automations canvas.
5,012 stars in the catalog
How they compare
| Tool | License | Self-host | Best for |
|---|---|---|---|
| Plunk Email | Not listed | Easy | Lists and transactional mail you host. |
| posta | GNU Affero General Public License v3.0 | Easy | Sending mail you already composed, not a visual campaign builder. |
| FluentCRM | Not listed | Easy | A WP site that wants CRM-ish campaigns without a new SaaS. |
| mailflare | GNU Affero General Public License v3.0 | Harder | Apex mail and a booking page, not a Klaviyo-style automations canvas. |
Related pages
- Plunk or Posta + Resend stack
- listmonk / Keila / Ghost stack
- Mailflare office stack
- Replace Mailchimp
- Replace Mailgun
- Replace SendGrid
- Replace Postmark
- Replace Substack
- Replace ConvertKit
- Replace beehiiv
- Replace Klaviyo
- Replace ActiveCampaign
- Replace Constant Contact
- Replace Brevo
- Replace Google Workspace
- Replace Microsoft 365
- Replace Calendly
- Replace Google Calendar
- All best open-source pages
- All replace pages
- All stacks
- Tools catalog
FAQ
- Why isn't listmonk in the list?
- The listmonk stack is public, but listmonk itself is not a listed Crew catalog row. This ranking only names catalog tools.
- Plunk or Mailflare?
- Plunk for the newsletter/SMTP job. Mailflare when you also want calendar and booking on a domain you own.
- Are these free?
- Open-source or fair-code; you still pay hosting and the SMTP/provider you send through. Template users never pay c17.
- How do I deploy it?
- Open /stacks/plunk-newsletter or /stacks/listmonk-email and copy the agent prompt. Railway CTAs stay on those pages.
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