Courier IMAP server

The Courier IMAP server is a fast, scalable, enterprise IMAP server that uses Maildirs. Many E-mail service providers use the Courier IMAP server to easy handle hundreds of thousands of mail accounts. With its built-in IMAP and POP3 aggregation proxy, the Courier IMAP server has practically infinite horizontal scalability. In a proxy configuration, a pool of Courier servers service initial IMAP and POP3 connections from clients. They wait to receive the client's log in request, look up the server that actually holds this mail account's mailbox, and establish a proxy connection to the server, all in a single, seamless process. Mail accounts can be moved between different servers, to achieve optimum resource usage. Courier IMAP supports communication protocols such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP.