smtpd(8) on Linux
The text ecbff36e84e6, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster) shipped it.
Simple Mail Transfer Protocol daemon
Flags it lists
-
-D -
-F -
-P -
-T -
-d -
-f -
-h -
-n -
-v