Courier MTA is a free, open-source integrated mail server offering ESMTP, IMAP, POP3, webmail, and mailing list services for POSIX systems.
Courier MTA is a free, open-source, integrated mail and groupware server created by developer S. Varshavchik, with the project's history dating back to 1998 and continuing to receive updates. It is licensed under the GNU General Public License and hosted on GitHub as a shared repository for its various sub-projects.
Unlike single-purpose mail transfer agents, Courier combines ESMTP, IMAP, POP3, webmail, and mailing list functionality in one consistent framework, letting administrators enable only the components they need for a given deployment.
Courier supports authentication via PAM, LDAP, PostgreSQL, or MySQL, virtual mail domains and accounts, maildir-based storage, DNS-based blacklists, SPF validation, message filtering, and TLS/SSL encryption. Its webmail module includes basic calendaring and scheduling.
The project favors strict RFC compliance over legacy Sendmail-style conventions, rejecting malformed messages rather than accommodating them, and compiles on most POSIX systems including Linux, BSD derivatives, Solaris, and AIX.
Courier MTA is free and open source under the GPL, with no commercial licensing tiers. Organizations bear only the cost of the infrastructure and system administration time needed to self-host and maintain it.
Yes, Courier MTA is free, open-source software distributed under the GNU General Public License.
No, they are unrelated. Courier MTA is an open-source mail server project dating to 1998; Courier (courier.com) is a separate, venture-backed notification API company founded in 2019.
It supports ESMTP, IMAP, POP3, LDAP, SSL/TLS, and HTTP for webmail, along with mailing list management.
It compiles on most POSIX-based systems, including Linux and BSD-derived kernels, as well as Solaris and AIX.
Yes, it supports virtual mail accounts and domains authenticated via LDAP, MySQL, or PostgreSQL.