How it plugs in
—Public API
NoOpen source
YesFree tier
Signal on Email Server Software4.9#27 of 33

Near it
All alternatives →- SMStalwart Mail Server#26 on this board
- RRabiMail#28 on this board
- SMSynology MailPlus Server#25 on this board
- CPCommuniGate Pro#29 on this board
- KKumoMTA#24 on this board
- EMEVO Mail Server#30 on this board
- WWhitemail#23 on this board
- GEGreenArrow Engine On-Premises#31 on this board
- Ggrommunio#22 on this board
- MSMailbux Self-Hosted#32 on this board