Full-Featured SMTP Servers
Postfix
Fast, easy to administer, and secure Sendmail replacement.- License: IPL-1.0
- Tech Stack: C, deb
Exim
Message transfer agent (MTA) developed at the University of Cambridge.- Source Code: git.exim.org
- License: GPL-3.0
- Tech Stack: C, deb
Sendmail
Message transfer agent (MTA).- License: Sendmail
- Tech Stack: C, deb
Enterprise Solutions
Courier MTA
Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services.- Source Code: courier-mta.org
- License: GPL-3.0
- Tech Stack: C, deb
Lightweight SMTP Servers
chasquid
SMTP (email) server with a focus on simplicity, security, and ease of operation.- Source Code: blitiri.com.ar
- License: Apache-2.0
- Tech Stack: Go
OpenSMTPD
Secure SMTP server implementation from the OpenBSD project.- Source Code: OpenBSD CVS
- License: ISC
- Tech Stack: C, deb
Haraka
Fast, highly extensible, and event driven SMTP server.- Source Code: GitHub
- License: MIT
- Tech Stack: Nodejs
DragonFly
A small MTA for home and office use. Works on Linux and FreeBSD.- Source Code: GitHub
- License: BSD-3-Clause
- Tech Stack: C
EmailRelay
A small and easy to configure SMTP and POP3 server for Windows and Linux.- Source Code: SourceForge
- License: GPL-3.0
- Tech Stack: C++
Specialized Solutions
OpenTrashmail
Complete trashmail solution that exposes an SMTP server and has a web interface to manage received emails. Works with multiple and wildcard domains and is fully file based (no database needed). Includes RSS feeds and JSON API.- Source Code: GitHub
- License: Apache-2.0
- Tech Stack: Python, PHP, Docker