With the Nightly Branch, it is now possible to use an external Identity Provider as an additional authentication source. mailcow utilizes the OIDC (OpenID Connect) protocol to authenticate only mailbox users. You can also get a SAL which is a one-time payment with no liabilities or returning fees. 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.
Spicebird is an open-source email and collaboration suite based on the Mozilla platform. It provides integrated e-mail, contacts, calendaring and instant messaging. It can connect to any SMTP/IMAP email server, CalDav Calendar server and Jabber serve