I remember that job and also building the server myself from scratch. Qmail, Squirrelmail, Dovecot and all that. It lasted about a year until we bought something as it was hell. Now days with IP reputation and spam filters - even if the server ran, you’d never get anything delivered outbound.

OP, the most I would do is an SMTP server that relays through Gmail for delivering alerts from monitoring systems. Anything else is pain.