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. Courier now also implements basic web-based calendaring and scheduling services integrated in the webmail module.
Certain parts of Courier (the mail filtering engine, the webmail server and IMAP server) are also available as separate, smaller, packages that can be used with other mail servers.
Features include:
- Implements SMTP extensions for mailing list management and spam filtering.
- Functions as an intermediate mail relay, relaying mail between an internal LAN and the Internet.
- Performs final delivery to mailboxes.
- Uses maildirs as its native mail storage format, but it can also deliver mail to legacy mailbox files as well.
- Configured by text files and Perl scripts.
- Dedicated web-based administration module.
Courier-IMAP’s features include:
- Extremely small footprint. On x86, Courier-IMAP’s main daemon is a fraction of the size of the UW-IMAP server, and has a greatly reduced memory footprint.
- Uses the Courier Authentication Library for authenticating mail accounts.
- Ability to restrict the maximum number of IMAP logins, and the maximum number of logins from the same IP address. This will prevent denial-of-service attacks where the attacker attempts to overload the server with multiple login connections.
- Shared folders. With additional server-side setup, folders can be shared between groups of accounts.
- IMAP over SSL. If OpenSSL or GnuTLS is installed, Courier-IMAP will, optionally, accept IMAP connections over SSL. The IMAP STARTTLS extension is also implemented.
- Authentication using SSL certificates.
- IPv6 support, if available.
- IMAP extensions that implement server-side sorting. This can be optionally disabled in environments that have limited resources.
- Courier-IMAP implements many popular IMAP protocol extensions that provide value-added functionality with most popular IMAP clients.
- Sorting and searching in non-English character sets.
- A compatible POP3 server is also included in the Courier-IMAP package, that uses the same authentication modules. The POP3 server can only access the INBOX, and cannot access any folders.
- An experimental mail access protocol, SMAP.
- IMAP/POP3 proxying. It is possible to distribute all mailboxes between multiple servers. A separate server (or a pool of servers) accepts all IMAP/POP3 connections, then connects to the right server based on the mailbox the connecting client is logging into.
Website: www.courier-mta.org
Support: Documentation
Developer: Sam Varshavchik
License: GNU General Public License v3.0
Courier Mail Server is written in C. Learn C with our recommended free books and free tutorials.
Return to Email | Return to Email Servers
| Popular series | |
|---|---|
 | The largest compilation of the best free and open source software in the universe. Each article is supplied with a legendary ratings chart helping you to make informed decisions. |
 | Hundreds of in-depth reviews offering our unbiased and expert opinion on software. We offer helpful and impartial information. |
 | Replace proprietary software with open source alternatives: Google, Microsoft, Apple, Adobe, IBM, Autodesk, Oracle, Atlassian, Corel, Cisco, Intuit, and SAS. |
 | Awesome Free Linux Games Tools showcases a series of tools that making gaming on Linux a more pleasurable experience. This is a new series. |
 | Machine Learning explores practical applications of machine learning and deep learning from a Linux perspective. We've written reviews of more than 40 self-hosted apps. All are free and open source. |
 | New to Linux? Read our Linux for Starters series. We start right at the basics and teach you everything you need to know to get started with Linux. |
 | Alternatives to popular CLI tools showcases essential tools that are modern replacements for core Linux utilities. |
 | Essential Linux system tools focuses on small, indispensable utilities, useful for system administrators as well as regular users. |
 | Linux utilities to maximise your productivity. Small, indispensable tools, useful for anyone running a Linux machine. |
 | Surveys popular streaming services from a Linux perspective: Amazon Music Unlimited, Myuzi, Spotify, Deezer, Tidal. |
 | Saving Money with Linux looks at how you can reduce your energy bills running Linux. |
 | Home computers became commonplace in the 1980s. Emulate home computers including the Commodore 64, Amiga, Atari ST, ZX81, Amstrad CPC, and ZX Spectrum. |
 | Now and Then examines how promising open source software fared over the years. It can be a bumpy ride. |
 | Linux at Home looks at a range of home activities where Linux can play its part, making the most of our time at home, keeping active and engaged. |
 | Linux Candy reveals the lighter side of Linux. Have some fun and escape from the daily drudgery. |
 | Getting Started with Docker helps you master Docker, a set of platform as a service products that delivers software in packages called containers. |
 | Best Free Android Apps. We showcase free Android apps that are definitely worth downloading. There's a strict eligibility criteria for inclusion in this series. |
 | These best free books accelerate your learning of every programming language. Learn a new language today! |
 | These free tutorials offer the perfect tonic to our free programming books series. |
 | Linux Around The World showcases usergroups that are relevant to Linux enthusiasts. Great ways to meet up with fellow enthusiasts. |
 | Stars and Stripes is an occasional series looking at the impact of Linux in the USA. |