opensmtpd - 7.5.0p0-1+b1 main

The OpenSMTPD server seeks to be
* as secure as possible, and uses privilege separation to mitigate
possible security bugs
* as reliable as possible: any accepted email must not be lost
* lean: it covers typical usage cases instead of every obscure one
* easy to configure, with a configuration syntax reminiscent of the OpenBSD
Packet Filter's (PF)
* fast and efficient: it can handle large queues with reasonable performance