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.
ESMTP over SSL is handled by the regular ESMTP daemon from courier-mta
in conjunction with the SSL/TLS wrapper supplied by courier-ssl.