smtpd(3tcl) on Linux
The text a7b8f1f568c9, as Debian 12 (Bookworm), Debian 11 (Bullseye) shipped it.
Tcl SMTP server implementation
Flags it lists
-
-banner -
-deliver -
-deliverMIME -
-validate_host -
-validate_recipient -
-validate_sender