The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP, TLS, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list services within a single, consistent, framework.

This package provides the functionality needed by all courier packages such as some configuration files, helper programs and the Courier TCP server daemon.

Courier uses the a TLS wrapper application named couriertls instead of embedding TLS support in the different applications. Additionally, this package contains a default set of trusted X.509 root CA certs.