Courier Mail Server

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Courier Mail Server
Basic data

developer Sam Varshavchik
Publishing year May 2000
Current  version 1.0.9
( August 29, 2019 )
operating system Unix ( POSIX )
programming language C ++
category Mail server
License GPL

The Courier Mail Server is a mail server and free software . It is primarily designed as a mail transfer agent and server for IMAP .

Courier saved in the maildir format of qmail from the beginning and introduced this for IMAP, while other servers initially stuck to mbox formats. With the development of Courier, Maildir was expanded to include folders and quotas, called Maildir ++.

The configuration is carried out using individual files or folders of the same name, from which the server reads all the files it contains. Many Courier configuration files can be broken down and recombined as needed. This enables a clear configuration for every scope.

The structure of Courier is modular. Maildrop , its mail delivery agent , and the modules for webmail and IMAP are also available separately for combination with other servers.


Courier MTA
the Mail Transfer Agent for Extended SMTP with emulation of Sendmail
Courier IMAP
the IMAP server
the SMAP server
the POP3 server
the mail delivery agent
Courier web admin
an HTML administration interface


The authentication of Courier may be coupled to the operating system, be based on its own database, and on the basis of external directories. It is processed by its own system service , which in turn can load modules for DBM , Pluggable Authentication Modules , MySQL , PostgreSQL and the Lightweight Directory Access Protocol .


The special feature of the SqWebMail module is that it is based directly on Maildir.


Courier's history began in 1997 with the approach that mail servers should detect and reject spam immediately. The first version of Courier was then developed in 1999 as a mail transfer agent for the Extended Simple Mail Transfer Protocol , parallel to the module for IMAP. Courier, along with UW IMAP and Cyrus, is one of the older three disclosed mail servers for large installations of IMAP. It is used, for example, by the University of Florida . The university contributed to further development at an early stage.


According to a study by Timo Sirainen, the Courier Mail Server is more secure than the UW IMAP and the Cyrus IMAP Server. In addition, the newer Dovecot software suite is geared towards security and has therefore been offering a premium on exploits since the beginning of 2006 .


Critics of the server accuse its author of not complying fully with the rules specified in the RFCs for the IMAP component (Courier-IMAP) . However, the author of the server denies this and describes the criticism as a smear campaign against his server because it was one of the first to implement the more efficient maildir format.

See also


Web links

Individual evidence

  1. . (accessed on September 6, 2019).
  2. Ubuntu manpage: makealiases . Canonical . Archived from the original on December 10, 2015. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved May 22, 2011. @1@ 2Template: Webachiv / IABot /
  3. Sam Varshavchik: Historical Background . Internet Archive. Archived from the original on April 5, 2001. Retrieved May 25, 2011.
  4. ^ CISE Mail Information . University of Florida. Retrieved May 15, 2011.
  5. Courier ChangeLog . Sam Varshavchik. Archived from the original on May 11, 2011. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved May 15, 2011. @1@ 2Template: Webachiv / IABot /
  6. C. Golubitsky: Toward an Automated Vulnerability Comparison of Open Source IMAP Servers (PDF; 160 kB) USENIX . Retrieved May 17, 2011.
  7. Security . Timo Sirainen. Retrieved August 7, 2013.
  8. Timo Sirainen: Security . Retrieved November 13, 2014.
  9. Sam Varshavchik: FUD . March 16, 2008. Retrieved December 18, 2010: “My response to claims that Courier-IMAP is not a compliant IMAP server is very simple: there was no such thing as a“ compliant ”IMAP server, because Crispin's IMAP specification makes that an impossible goal. "