7.1 qmail Architecture

Several different qmail components play roles in receiving messages from the Internet. Messages from the Internet typically enter the mail server via the qmail-smtpd daemon, which listens on port 25 and conducts the SMTP transaction with the remote sender. qmail-smtpd passes the messages to the qmail-queue program, which stores them in an outgoing queue for further processing. The qmail-send daemon reads the messages in the outgoing queue and attempts to deliver them using either the qmail-lspawn daemon (which passes it to the qmail-local program for local delivery) or the qmail-rspawn daemon (which passes them to the qmail-remote program for relaying to remote hosts ). Figure 7-1 illustrates the flow of email through qmail components.

Figure 7-1. qmail architecture during message receipt

Most systems keep all of qmail's files in /var/qmail . Configuration files reside in /var/qmail/control .