Update README.md

README.md

@@ -250,6 +250,7 @@ Some [Groupware](#groupware) solutions also feature calendar/address book editin
 _simple deployment of a mail server, e.g. for inexperienced or impatient admins._
 
   * [Citadel](http://www.citadel.org/) - Feature packed, easy, versatile, and powerful mail server, thanks to exclusive "rooms" based architecture. ([Source Code](http://code.citadel.org/?p=citadel.git;a=summary)) `GPLv3` `C`
+  * [docker-mailserver](https://github.com/tomav/docker-mailserver) - A fullstack but simple mail server (smtp, imap, antispam, antivirus). Only configuration files, no SQL database. Keep it simple and versioned. Easy to deploy and upgrade. ([Source Code](https://github.com/tomav/docker-mailserver)) `MIT` `Docker`
   * [iRedMail](http://www.iredmail.org/) - Full-featured mail server solution based on Postfix and Dovecot. ([Source Code](https://bitbucket.org/zhb/iredmail/commits/)) `GPLv3` `Shell`
   * [Mailcow](https://mailcow.email/) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. ([Source Code](https://github.com/andryyy/mailcow)) `GPLv2` `PHP`
   * [Mail-in-a-Box](https://mailinabox.email/) - Turns any Ubuntu server into a fully functional mail server with one command. ([Source Code](https://github.com/mail-in-a-box/mailinabox)) `CC0` `Shell`