4837 shaares
Cypht supports TOTP 2fa, CardDAV, PGP, and Sieve
Snappymail is a secured fork of Rainloop
iRedMail: all-in-one mail system, available as FreeBSD package
Isotope installs and runs through Docker
Horde was abandoned in 2017
NOCC and SquirrelMail work but are very primitive
