Posthorn

Judgement

What it is

Integration

What it does

A gateway that accepts mail from your self-hosted apps by HTTP form, HTTP API or SMTP and forwards it to Postmark, Resend, Mailgun, SES or SMTP, configured in one TOML file.

Adopt it when

A homelab or small team runs several apps that each need outbound email and wants one place to configure it.

Watch out

Six months old with a single author.

Ready for

Usable

Runs as

Self-hosted server

Built with

Go

How established

Young: started 6 months ago, latest release v2.0.1.

What the license allows

You can build it into a product you sell, as long as you keep its copyright notice.

Judged on 2026-11-03 from the project's README and GitHub data. The license and age lines are worked out directly.

Built from

Follow it down: Posthorn → Go → runs on a microchip

How compilers were built, back to punched paper tape

Open-source alternatives to Posthorn

1. 1
   React Email resend

   💌 Build and send emails using React

   Developer tool Production-ready Your team writes React and wants maintainable, previewable email templates for any sending provider.

   ★ 20k MIT TypeScript Active, pushed 3 days ago
2. 2
   MJML mjmlio

   MJML: the only framework that makes responsive email easy

   Framework or platform Production-ready Anyone who hand-codes HTML emails and wants them to render in Outlook and Gmail without table hacks.

   ★ 18k MIT JavaScript Active, pushed 10 days ago
3. 3
   Postal postalserver

   📮 A fully featured open source mail delivery platform for incoming & outgoing e-mail

   Complete system Production-ready You send large volumes of transactional email and want your own Sendgrid-style platform on your own IPs.

   ★ 17k MIT Ruby Active, pushed 4 days ago
4. 4
   Plunk useplunk

   The Open-Source Email Platform

   Complete system Usable You want one open-source tool for both product emails and newsletters on AWS SES.

   ★ 5.6k AGPL-3.0 TypeScript Active, pushed 2 days ago
5. 5
   React Email Editor unlayer

   Drag-n-Drop Email Editor Component for React.js

   Integration Production-ready Your product needs users to design emails or newsletters inside it.

   ★ 5.3k MIT TypeScript Active, pushed 2 days ago
6. 6
   useSend usesend

   Open source alternative to Resend, Sendgrid, Postmark etc.

   Complete system Usable You want Resend or Postmark convenience at SES prices, hosted or self-hosted.

   ★ 4.8k AGPL-3.0 TypeScript Active, pushed 3 days ago
7. 7
   Posta goposta

   Self-hosted email delivery platform that enables applications to send emails via HTTP APIs while handling SMTP delivery, templates, storage, security, and analytics. Fully self-hostable alternative to services like SendGrid or Mailgun.

   Complete system Experimental You want your apps' transactional email behind one self-hosted API with logs and templates.

   ★ 633 AGPL-3.0 Go Active, pushed yesterday
8. 8
   Mrml jdrouet

   Implementation of mjml in rust

   Building block Usable You render MJML at high volume or outside Node.js and want speed.

   ★ 510 MIT HTML Active, pushed 17 days ago

Commercial email sending platforms and email templating tools

1. 1
   SendGrid Twilio

   SendGrid's trusted email API and marketing campaigns platform is now available through Twilio.com.

   Building block Production-ready An application needs to send high volumes of email through a well-known API.

   283 readers a month Since 2009 Commercial
2. 2
   Amazon SES Amazon Web Services

   Amazon Simple Email Service (SES) is a cost-effective, flexible, and scalable email service provider that allows developers to send email from within any application.

   Building block Production-ready You send large volumes of email, run on AWS and can manage deliverability yourself.

   Commercial
3. 3
   Mailgun Sinch

   Powerful Transactional Email APIs that enable you to send, receive, and track emails, built with developers in mind. Learn more today!

   Building block Production-ready Developers need to send transactional email and also parse inbound email into their application.

   64 readers a month Since 2010 Commercial
4. 4
   Postmark ActiveCampaign

   Send transactional and marketing emails and get them to the inbox on time, every time. Postmark is a fast and reliable email delivery service for developers.

   Building block Production-ready Password resets, receipts and other critical app email must arrive quickly and reliably.

   Commercial
5. 5
   Resend Resend

   The best way to reach humans instead of spam folders. Deliver transactional and marketing emails at scale.

   Building block Usable A modern web app team, especially using React and Next.js, wants a clean email API that is quick to integrate.

   Commercial