Courier mail server

                  The Courier mail server is a mail transfer agent (MTA) server that provides ESMTP, IMAP, POP3, SMAP, webmail, and mailing list services with individual components. It is best known for its IMAP server component.

                Courier can function as an intermediate mail relay, between an internal LAN and the Internet, or perform final delivery to mailboxes. Courier uses maildirs as its native storage format and can also deliver mail to legacy mailbox files. Configuration files are in plain text format and may include Perl scripts.Courier can provide mail services for regular operating system accounts. Courier can also provide mail services for virtual mail accounts, managed by any of LDAP directory service, Berkeley DB, MySQL or PostgreSQL authentication database.
 
              Parts of Courier, such as the maildrop filtering system, the webmail and IMAP server, can also be installed as independent packages which can be used with other mail servers. Courier-IMAP is a particularly popular combination with Qmail, Exim, and Postfix servers that are configured to use maildirs.Courier's source compiles on most POSIX-based operating systems based on Linux and BSD-derived kernels. It uses SMTP extensions for list management and spam filtering.A review of SourceForge on February 24, 2009 indicates that Courier had been downloaded from that site over 1,000,000 times ranking 282nd on all packages with numerous third-party applications

              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. Individual components can be enabled or disabled at will. The Courier mail server now implements basic web-based calendaring and scheduling services integrated in the webmail module. Advanced groupware calendaring services will follow soon.

            The Courier mail server's source code should compile on most POSIX-based operating systems based on Linux, and BSD-derived kernels. The Courier mail server should also compile on Solaris and AIX, with some help from Sun's or IBM's freeware add-on tools for their respective operating systems.
The Courier mail server evolved out of several related projects, that merged together (more on that later). The Courier mail server implements SMTP extensions for mailing list management and spam filtering. The Courier mail server can function as an intermediate mail relay, relaying mail between an internal LAN and the Internet, or perform final delivery to mailboxes. The Courier mail server uses maildirs as its native mail storage format, but it can also deliver mail to legacy mailbox files as well. The Courier mail server's configuration is set by plain text files and Perl scripts. Most of The Courier mail server's configuration can now be adjusted from a web browser, using The Courier mail server's web-based administration module.
The Courier mail server can provide mail services for regular operating system accounts. The Courier mail server can also provide mail services for virtual mail accounts, managed by an LDAP, MySQL, or PostgreSQL-based authentication database.