How to: Mail Servers
*Mail Delivery Agents (IMAP/POP3 software).*

* [Courier IMAP/POP3](http://www.courier-mta.org/imap/) - Fast, scalable, enterprise IMAP and POP3 server.
* [Cyrus IMAP/POP3](http://cyrusimap.org/) - Intended to be run on sealed servers, where normal users are not permitted to log in.
* [Dovecot](http://www.dovecot.org/) - IMAP and POP3 server written primarily with security in mind.
* [Qpopper](http://www.eudora.com/products/unsupported/qpopper/) - One of the oldest and most popular server implementations of POP3.

*Mail Transfer Agents (SMTP servers).*

* [Exim](http://www.exim.org/) - Message transfer agent (MTA) developed at the University of Cambridge.
* [Haraka](http://haraka.github.io/) - A high-performance, pluginable SMTP server written in JavaScript.
* [MailCatcher](http://mailcatcher.me/) - Ruby gem that deploys a simply SMTP MTA gateway that accepts all mail and displays in web interface. Useful for debugging or development.
* [Maildrop](https://github.com/m242/maildrop) - Open Source disposable email SMTP server, also useful for development.
* [OpenSMTPD](https://opensmtpd.org/) - Secure SMTP server implementation from the OpenBSD project.
* [Postfix](http://www.postfix.org/) - Fast, easy to administer, and secure Sendmail replacement.
* [Qmail](http://cr.yp.to/qmail.html) - Secure Sendmail replacement.
* [Sendmail](http://www.sendmail.com/sm/open_source/) - Message transfer agent (MTA).

*Complete solutions.*

* [Mail-in-a-Box](https://mailinabox.email/) - Take back control of your email with this easy-to-deploy mail server in a box.
* [iRedMail](http://www.iredmail.org/) - Full-featured mail server solution based on Postfix and Dovecot.