Configuration of Postfix

Postfix was created as a replacement for sendmail, and therefore it maintains a mostly “sendmail-compatible” interface. In most cases, postfix can act as a drop-in replacement for sendmail, and scripts that had called sendmail directly with various command-line options will continue to work. Postfix accomplishes this by including with its distribution a program called /usr/sbin/sendmail, which exists to act as a “bridge” between calls to sendmail and the postfix utility. Because of this, many of the commands you are used to in sendmail will work with postfix:

# which sendmail
# for file in /usr/sbin/sendmail /usr/bin/mailq /usr/bin/newaliases; { echo -n
"$file: " && rpm -q --whatprovides ${file}; }
/usr/sbin/sendmail: postfix-2.3.2-32
/usr/bin/mailq: postfix-2.3.2-32
/usr/bin/newaliases: postfix-2.3.2-32

The postfix system is made up of a number of different applications, as opposed to the monolithic nature of sendmail. The main program is /usr/lib/postfix/master, which is the daemon that listens on TCP port 25 for incoming SMTP connections and accepts mail. Other applications are listed in Table 17-1. These applications live in /usr/lib/postfix/ unless otherwise indicated.

Table 17-1. Postfix programs

Program name



Maintains statistics about client connection counts or client request rates. This information can be used to defend against clients that hammer a server with either too many simultaneous sessions or too many successive ...

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