Indeed. qmail describes this quite well and is portable for unix. The qmail-queue process does local deliveries, tcpserver runs against port 25 and invokes qmai

Indeed. qmail describes this quite well and is portable for unix. The qmail-queue process does local deliveries, tcpserver runs against port 25 and invokes qmail-smtpd. Spending time to design software into small components pays for itself in the long run. I think qmail's downfall was that it is so stable people dind't have many issues to fix once the patches were written. It is starting to reform in 'notqmail', which I'm hoping will spar with postfix.