The Courier mail server is a mail transfer agent

Mail transfer agent

Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...

 (MTA) server that provides ESMTP, IMAP, POP3, SMAP

Simple Mail Access Protocol

The Simple Mail Access Protocol is an application layer Internet protocol for accessing e-mail stored on a server. It was introduced as part of the Courier suite, with the goal of creating a simpler and more capable alternative to IMAP....

, webmail, and mailing list

Electronic mailing list

An electronic mailing list is a special usage of email that allows for widespread distribution of information to many Internet users. It is similar to a traditional mailing list — a list of names and addresses — as might be kept by an organization for sending publications to...

 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 maildir

Maildir

The Maildir e-mail format is a common way of storing e-mail messages, where each message is kept in a separate file with a unique name, and each folder is a directory...

s 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

Perl

Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...

 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

Lightweight Directory Access Protocol

The Lightweight Directory Access Protocol is an application protocol for accessing and maintaining distributed directory information services over an Internet Protocol network...

 directory service, Berkeley DB

Berkeley DB

Berkeley DB is a computer software library that provides a high-performance embedded database for key/value data. Berkeley DB is a programmatic software library written in C with API bindings for C++, PHP, Java, Perl, Python, Ruby, Tcl, Smalltalk, and most other programming languages...

, MySQL

MySQL

MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...

 or PostgreSQL

PostgreSQL

PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...

 authentication database.

Parts of Courier, such as the maildrop

Maildrop

maildrop is a Mail delivery agent used by the Courier Mail Server. The maildrop MDA also includes filtering functionality.maildrop receives mail via stdin and delivers in both Maildir and mbox formats....

 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

Qmail

qmail is a mail transfer agent that runs on Unix. It was written, starting December 1995, by Daniel J. Bernstein as a more secure replacement for the popular Sendmail program...

, Exim

Exim

Exim is a mail transfer agent used on Unix-like operating systems. Exim is free software distributed under the terms of the GNU General Public License, and it aims to be a general and flexible mailer with extensive facilities for checking incoming e-mail....

, and Postfix

Postfix (software)

In computing, Postfix is a free and open-source mail transfer agent that routes and delivers electronic mail. It is intended as a fast, easier-to-administer, and secure alternative to the widely-used Sendmail MTA....

 servers that are configured to use maildirs.

Courier's source compiles on most POSIX

POSIX

POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...

-based operating systems based on Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 and BSD-derived kernels. It uses SMTP extensions for list management and spam filtering.

A review of SourceForge

SourceForge

SourceForge Enterprise Edition is a collaborative revision control and software development management system. It provides a front-end to a range of software development lifecycle services and integrates with a number of free software / open source software applications .While originally itself...

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

External links

• Courier-MTA website
• Installing and configuring Courier-IMAP
• Setting up a mail server - includes Courier as the IMAP component