7.1 Accepting Incoming SMTP Mail

Chapter 4 discussed the basic setup of the SMTP daemon in /service/qmail-smtpd. The supervise daemon runs tcpserver, which listens for incoming connections, then runs qmail-smtpd to run the SMTP session and queue the received mail. The control file rcpthosts lists the domains for which it accepts mail. (If that file doesn't exist, it accepts mail for all domains and can be an open relay, which spammers see as an open invitation to abuse.)

The normal SMTP setup consults a tcprules file that lists the IP addresses from which to accept and deny connections. The rules file is /var/qmail/rules/smtprules.txt, which is compiled into the binary /var/qmail/rules/smtprules.cdb that tcpserver consults.