sendmail, 4th Edition

A Quick Tour

The other commands in a configuration file tend to be more complex than the version command you just saw (so complex, in fact, that whole chapters in this book are dedicated to most of them). Here, we present a quick tour of each command—just enough to give you the flavor of a configuration file but in small enough bites to be easily digested.

Mail delivery agents

Recall that the sendmail program does not generally deliver mail itself. Instead, it calls other programs to perform that delivery. The M command defines a mail delivery agent (a program that delivers the mail). For example, as was previously shown:

Mlocal,         P=/usr/lib/mail.local, F=lsDFMAw5:/|@qPSXfmnz9,
                S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,
                T=DNS/RFC822/SMTP,
                A=mail.local -l

This tells sendmail that local mail is to be delivered by using the /usr/lib/mail.local program. The other parameters in these lines are covered in Chapter 20 on page 711.

Macros

The ability to define a value once and then use it in many places makes maintaining your sendmail.cf file easier. The D sendmail.cf command defines a macro. A macro’s name is either a single letter or curly-brace-enclosed multiple characters. It has text as a value. Once defined, that text can be referenced symbolically elsewhere:

DRmail.us.edu           ← a single letter
D{REMOTE}mail.us.edu    ← multiple characters (beginning with V8.7)

Here, R and {REMOTE} are macro names that have the string mail.us.edu as their values. Those values are accessed elsewhere in the sendmail.cf