It listens to the network for incoming mail, transports mail messages to
other machines, and hands local mail to a local program for local delivery. It can
append mail to files and pipe mail through other programs. It can queue mail for
later delivery and understand the aliasing of one recipient name to another.
1.6.1 Role in the Filesystem
The sendmail program??™s role (position) in the local filesystem hierarchy can be
viewed as an inverted tree (see Figure 1-3).
When sendmail is run, it first reads the /etc/mail/sendmail.cf configuration file.
Among the many items contained in that file are the locations of all the other files
and directories that sendmail needs.
Figure 1-2. A simplified conversation
hello
mail from sender
mail to friend2@remote
Here comes the message
Done
Remote Sendmail Says:
hello
OK
OK
OK
OK
Local Sendmail Says:
This is the Title of the Book, eMatter Edition
Copyright ?© 2007 O??™Reilly & Associates, Inc. All rights reserved.
1.6 Basic Roles of sendmail | 11
Files and directories listed in sendmail.cf are usually specified as full pathnames for
security (suchas /var/spool/mqueue rather than mqueue). As the first step in our tour
of those files, run the following command to gather a list of them:*
% grep =/ /etc/mail/sendmail.cf
The output produced by the grep(1) command might appear something like the
following:??
O AliasFile=/etc/mail/aliases
#O ErrorHeader=/etc/mail/error-header
O HelpFile=/etc/mail/helpfile
O QueueDirectory=/var/spool/mqueues/q.
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