Top 8 Mail Transfer Agent Open-Source Projects

Postal

42 14,116 9.6 Ruby

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

Project mention: Postal: Open-source mail delivery platform for incoming and outgoing email | news.ycombinator.com | 2024-03-13

Haraka

16 4,824 7.5 JavaScript

A fast, highly extensible, and event driven SMTP server

Project mention: postale.io? Is this legit? Email hosting unlimited domains. | /r/webhosting | 2023-06-17

postale.io has an MX record that points to mail.postale.io, which resolves to an AWS IP address (probably an EC2 instance) and has Haraka listening on port 25 (if its SMTP banner can be believed)

InfluxDB

www.influxdata.com sponsored

Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
Exim

9 699 9.2 C

Exim Mail Transport Agent - source, testsuite and documentation

Project mention: Is it right to blame Google/Yahoo for deprecating an email forwarding service? | news.ycombinator.com | 2024-01-14

Documentation for ARC is pretty sparse.
The instructions for setting it up in Exim (default MTA on Debian systems) can be found here: https://github.com/Exim/exim/blob/master/doc/doc-txt/experim...
(AFAICT, there is absolutely no mention of ARC in the main Exim documentation: https://exim.org/docs.html)

OpenSMTPD

18 475 9.1 C

This is official OpenSMTPD Portable repository. Forks, pull requests and other contributions are welcome!

Project mention: OpenBSD acme-client で Let's Encrypt 証明書を取得する | dev.to | 2023-09-09

Slimta

1 170 2.8 Python

Python libraries to send, receive, and queue email.
Courier MTA

5 70 7.1 C

Courier Mail Server
Find-Us-On-GitLab

0 0 0.0

Lightmeter uses GitLab, not GitHub -- find repos at: https://gitlab.com/lightmeter
WorkOS

workos.com sponsored

The modern identity platform for B2B SaaS. The APIs are flexible and easy-to-use, supporting authentication, user identity, and complex enterprise features like SSO and SCIM provisioning.
Qmail

0 0 0.0

Bind to different local ip addresses depending on the domain part of the sender argument when using `qmail-remote`.

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020).