When you enable the local delivery agent with:

MAILER(`local')

you are really enabling two delivery agents—local and prog. The local delivery agent is charged with local, final delivery to a user's mailbox. The prog delivery agent is used to pipe mail through programs.

The local delivery agent

The local delivery agent's job is to deliver mail to its final destination in the user's mailbox. Its name doesn't tell you what program is actually run to perform that delivery, but it is usually either /bin/mail or /usr/libexec/mail.local, although it could also be procmail or spop.

The program you select to perform the role of final delivery will determine the defaults that this delivery agent starts with. If you need to change any of those defaults, you can first determine what they are by looking in your configuration file for the Mlocal lines. They might look like this, for example:

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

You can use any of the mc configuration macros shown in Table 20-7 to modify or replace these defaults.

Note that mc configuration macro definitions must always precede the MAILER declaration to which they relate.

The prog delivery agent

The prog delivery agent is used to send mail through programs for final delivery (see Section 12.2.3 for a discussion of this process as it relates to the "|prog" form of aliases). The prog delivery agent is co-declared with the local delivery agent by this MAILER declaration:

MAILER(`local')

The prog delivery agent does not actually run programs itself. Instead, it executes a program that is expert at running other programs. In general, that program is the Bourne shell, /bin/sh. But it as easily can be other shells or programs, such as smrsh(8) (Section 5.8) or ksh(1). To find the defaults defined for your site, look in the sendmail.cf file for a line that begins with Mprog:

Mprog,    P=/bin/sh, F=lsDFMoqeu9, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL, D=$z:/,
          T=X-Unix/X-Unix/X-Unix,
          A=sh -c $u

You can use any of the mc configuration macros shown in Table 20-8 to modify or replace these defaults.

Note that mc configuration macro definitions must always precede the MAILER declaration to which they relate.