1.flectar / mail
Built from the ground up for speed. Flectar Mail delivers native performance, instant startup, and as little as 80 MB of RAM.
+109 stars
from 1,616 · score 4.70
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2.mailcow / mailcow-dockerized
mailcow: dockerized - 🐮 + 🐋 = 💕
+33 stars
from 13,694 · score 3.53
3.Alinto / sogo
SOGo is a very fast and scalable modern collaboration suite (groupware). It offers calendaring, address book management, and a full-featured Webmail client along with resource sharing and permission handling. It also makes use of documented standards (IMAP, CalDAV, CardDAV, etc.) and thereby provides native connectivity (without plugins) to many clients such as Microsoft Outlook, Apple iCal, the iPhone, Mozilla Lightning, and a plethora of mobile devices.
+6 stars
from 2,176 · score 1.95
4.Intermesh / groupoffice
Group Office groupware and CRM
+1 stars
from 283 · score 0.69