Open source mail transfer agent developed since 1995 at the University of Cambridge by Philip Hazel, under the GPL. The default MTA on Debian and widespread on shared hosting through cPanel. Highly configurable thanks to its routing rules and ACL language.
Ecosystem directory
Organizations, events and solutions of the email ecosystem. Every entry is verified and dated.
MTA servers
Mail server software (MTAs), open source or commercial, that routes messages between domains.
US commercial MTA bundled with a campaign management interface (GreenArrow Studio), aimed at senders and publishers hosting their own sending infrastructure. Handles per-destination queues, bounces, feedback loops and throttling.
Swedish commercial MTA platform, scriptable in a dedicated language, used by hosting companies, operators and sending platforms for inbound and outbound mail. Natively integrates DKIM, ARC, DMARC and MTA-STS and connects to common anti-spam and anti-virus engines.
Open source SMTP server written in Node.js, created in 2011 by Matt Sergeant under the MIT licence. Fully plugin-based architecture designed for high-throughput inbound and outbound mail processing. Used notably as a receiving and filtering front end.
Open source MTA launched in 2023 by a team with a background at the makers of PowerMTA and Momentum, written in Rust and scriptable in Lua, under the Apache 2.0 licence. Designed for very high volume sending with per-domain queues, bounce handling and monitoring integrations. Commercial support offered by the vendor.
Commercial MTA developed by Copernica in Amsterdam, built around a RabbitMQ queue for injection and JSON result reporting. Web interface for managing queues and per-recipient-domain policies, aimed at sending platforms and large senders.
Commercial Windows mail server published since 1996 by Alt-N Technologies (Texas). Aimed at SMBs, it bundles SMTP, IMAP, webmail, calendaring and security features (anti-spam, anti-virus, SPF, DKIM and DMARC authentication).
Open source SMTP server from the OpenBSD project, under the ISC licence, started in 2008 with a focus on simple configuration and security. Available on the BSDs and Linux, suited to modest servers and outbound relays. Handles TLS, alias tables and plugin-based filtering.
Open source mail transfer agent created in 1998 by Wietse Venema as an alternative to Sendmail, under the IBM Public License and later the EPL. The default MTA of many Linux distributions, valued for its modular architecture and security. Handles inbound and outbound SMTP, queues, policies and filters.
Commercial MTA developed by Port25 Solutions from 1999, acquired by SparkPost in 2017 and now part of Bird. A reference for high-volume senders thanks to its fine-grained per-domain queues, virtual IPs and recipient response handling, with detailed event reporting (accounting).
The historical Unix MTA, written by Eric Allman in the early 1980s and long dominant on the Internet. Still maintained as open source; Sendmail Inc. was acquired by Proofpoint in 2013. Known for its complex configuration file and its Milter filtering interface, adopted by other MTAs.
Missing or inaccurate entry? Suggest a correction.