OpenSMTPD
A free SMTP server from the OpenBSD project for sending and receiving email.
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About OpenSMTPD
OpenSMTPD is an implementation of the server-side SMTP protocol defined in RFC 5321, with some standard extensions. It lets an ordinary machine exchange email with other mail servers. It was started out of dissatisfaction with other implementations and is part of the OpenBSD project.
It is primarily developed by Gilles Chehade and Eric Faurot with contributions from OpenBSD developers and others. Version 7.8 came out in October 2025, with a portable 7.8.0p1 release in March 2026. It suits administrators who want a smaller, simpler mail server.
Strengths
- Part of the OpenBSD project
- Simpler than many other SMTP servers
- Permissive ISC license
- Regular releases, including a portable version
Limitations
- A mail server, not a client for reading email
- Needs other components for a complete mail setup
Details
- Pricing
- FreeFree and open source under the ISC license.
- License
- ISC
- Developer
- The OpenBSD Project
- Platforms
- Linux, Self-hosted, Command line
- How it runs
- Downloadable app, Self-hosted
- Account
- Not required
- Best suited for
- Administrators who want a simple SMTP server on OpenBSD or Linux
- Categories
- Email clients, IT administration
- Last verified
- Added
- Provenance
- Facts checked against the developer's own pages and store listings, 1 sources on file.
Alternatives to OpenSMTPD
Compare allSoftware that can replace OpenSMTPD for an important use case, and what changes if you switch.
Postfix
A widely used open-source mail transfer agent for routing and delivering email.
Postfix is a widely used, security-focused MTA packaged by most operating systems with extensive documentation, though its configuration requires more mail server knowledge.
Exim
An open-source mail transfer agent for Unix systems with flexible routing and mail checking.
Exim is a GPL-licensed MTA with very flexible routing and extensive checks for incoming mail, but its configuration is more complex than OpenSMTPD's.
Mox
An all-in-one open-source mail server for low-maintenance self-hosted email.
Mox replaces the SMTP server and adds IMAP, webmail, automatic TLS and junk filtering in one program, though it is younger and less widely deployed.
Similar software
Related functionality, not necessarily a direct replacement.
Dovecot
An open-source IMAP and POP3 server that stores mailboxes and serves them to mail clients.
Cyrus IMAP
An open-source email, contacts and calendar server with IMAP, JMAP, CalDAV and CardDAV support.
Mailu
A full-featured self-hosted mail server delivered as a set of Docker images.
docker-mailserver
A complete mail server with SMTP, IMAP, antispam and antivirus, packaged as a single container.
Google Postmaster Tools
Google's web dashboard for checking a sending domain's reputation and mail deliverability to Gmail.
