"This chapter describes how Postfix works, what each piece of
the system does, and how these components relate to each other.
After going through this material, you should have an understanding
of Postfix as a whole, so that you can focus on individual
"Postfix consists of a small number of programs that interact
with user processes (sendmail, postqueue, postsuper, and so on) and
a larger number of programs that run in the background. Only the
programs that run in the background are controlled by the master
daemon. The master daemon's job is to determine what work there is
to do and dispatch the appropriate program to do the work. This
modular design allows for a higher level of security because each
program runs with the lowest privilege set needed to fulfill its
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