The Courier mail transfer agent (MTA) is an integrated mail/groupware
server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP,
SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list
services within a single, consistent, framework.
Courier uses the a SSL/TLS wrapper application named
couriertls instead of embedding SSL/TLS support in the different applications.
Additionally, this package contains a default set
of trusted X.509 root CA certs.