Please consider a support contract (around 30 € per month) with Servercow to support further development. We support you while you support us. :)
Or just spread the word: moo.
Please see the official documentation for instructions.
Important: mailcow makes use of various open-source software. Please assure you agree with their license before using mailcow. Any part of mailcow itself is released under GNU General Public License, Version 3.