A lightweight mail server with SMTP and POP3 support. It mainly used as store-and-forward mail server with POP access to spooled messages or it can be used as a personal internet mail server.
Courier-MTA Alternatives
Courier-MTA is described as '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' and is a Mail Server in the office & productivity category. There are more than 10 alternatives to Courier-MTA for a variety of platforms, including Linux, Mac, Windows, BSD and Self-Hosted apps. The best Courier-MTA alternative is Postfix, which is both free and Open Source. Other great apps like Courier-MTA are Mail-in-a-box, Exim, OpenSMTPD and Sendmail.