Top pick · highest health
OpenSMTPD
Secure SMTP server implementation from the OpenBSD project.
★ 586 57 commits / 90d ⟳ 2 months ago ISC
Category
Open source communication - email - mail transfer agents
Mail Transfer Agents (MTAs) - SMTP servers. This page ranks 9 open-source mail transfer agents projects by a health score recomputed every night from repository data; nothing else affects the order. OpenSMTPD leads at 81/100 with 57 commits in the last 90 days and 586 stars, followed by Haraka (71) and DragonFly (21). 2 of the 9 score 70 or above, 0 publish a Docker image, and the median health is 10. GPL-3.0 is the most common licence, carried by 3 of them. Between them they stand in for SendGrid. The score weighs commits in the last 90 days, release recency, stars, archive status and Docker support; a low number means low measurable activity, not low quality, so a finished, stable tool can legitimately sit lower down.
updated Oct 2026 9 tools ★ 6.5k stars 0 with Docker median 10
Best for…
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Most starred
5,629 stars on GitHub, the largest community in the category.
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Most active
57 commits in the last 90 days, the fastest-moving codebase here.
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Most permissive
BSD-3-Clause licence with health 21/100: the strongest option if you need to embed or fork commercially.
Ranked by health
Table view
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DragonFly
A small MTA for home and office use. Works on Linux and FreeBSD.
★ 266 1 commits / 90d ⟳ 2 months ago BSD-3-Clause
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chasquid
SMTP (email) server with a focus on simplicity, security, and ease of operation.
★ 0 0 commits / 90d ⟳ unknown Apache-2.0
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Courier MTA
Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services.
★ 0 0 commits / 90d ⟳ unknown GPL-3.0
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EmailRelay
A small and easy to configure SMTP and POP3 server for Windows and Linux.
★ 0 0 commits / 90d ⟳ unknown GPL-3.0
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Exim
Message transfer agent (MTA) developed at the University of Cambridge.
★ 0 0 commits / 90d ⟳ unknown GPL-3.0
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Postfix
Fast, easy to administer, and secure Sendmail replacement.
★ 0 0 commits / 90d ⟳ unknown IPL-1.0
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| # | ||||||
|---|---|---|---|---|---|---|
| 1 | OpenSMTPD | 586 | 57 | ISC | 2 months ago | |
| 2 | Haraka | 5.6k | 18 | MIT | today | |
| 3 | DragonFly | 266 | 1 | BSD-3-Clause | 2 months ago | |
| 4 | chasquid | 0 | 0 | Apache-2.0 | unknown | |
| 5 | Courier MTA | 0 | 0 | GPL-3.0 | unknown | |
| 6 | EmailRelay | 0 | 0 | GPL-3.0 | unknown | |
| 7 | Exim | 0 | 0 | GPL-3.0 | unknown | |
| 8 | Postfix | 0 | 0 | IPL-1.0 | unknown | |
| 9 | Sendmail | 0 | 0 | Sendmail | unknown |
How the mail transfer agent tools compare
OpenSMTPD edges Haraka 81 to 71, and most of the difference is commit activity: 57 commits in 90 days against 18 commits in 90 days. Haraka has the largest following at 5.6k stars, yet ranks #2 of 9, held back mostly by commit activity (18 commits in 90 days).
The most recent release is Haraka v3.3.5, published 13 days ago. DragonFly publishes no tagged releases, which costs up to 25 of the 100 points. DragonFly scores under 40, so check recent activity before adopting it. By stack, C (6), C++ (1) and Go (1) are the most common. OpenSMTPD, Haraka, DragonFly and 1 more are permissively licensed; Courier MTA, EmailRelay and Exim are copyleft. chasquid, Courier MTA, EmailRelay and 3 more are not hosted on a forge Repoly can read, so they have no measured score yet.
Communication - Email - Mail Transfer Agents: common questions
What is the best open source mail transfer agent tool?
By Repoly's GitHub health score, OpenSMTPD at 81/100 (57 commits in 90 days, 7.9.0p0 from 2 months ago). Haraka is next at 71; OpenSMTPD's lead comes mostly from commit activity. The score measures maintenance, not features, so shortlist the top few and try them.
Which mail transfer agent tools are the most actively developed?
OpenSMTPD (57 commits in 90 days), Haraka (18 commits in 90 days) and DragonFly (1 commits in 90 days). Commit activity is 35 of the 100 health points, the largest single term.
Which mail transfer agent tools can I run in Docker?
None of the 9 advertise Docker support, so plan for a native install.
Which mail transfer agent tools have a permissive licence?
4 of 9: OpenSMTPD (ISC), Haraka (MIT), DragonFly (BSD-3-Clause), chasquid (Apache-2.0). 3 are copyleft.
Which paid products can open source mail transfer agent tools replace?
SendGrid (Haraka ranks highest here).
