Jami

A small and easy to configure SMTP and POP3 server for Windows and Linux.

Spectrum 2 is an open source instant messaging transport. It allows users to chat together even when they are using different IM networks.

Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services.

Your Debian-based data center in a box. A set of general-purpose Ansible roles that can be used to manage Debian or Ubuntu hosts.

Luke Smith's bash script to completely automate the setup of a Postfix/Dovecot/SpamAssassin/OpenDKIM server on debian.

Message transfer agent (MTA) developed at the University of Cambridge.