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Delivery Agents
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30.2 The Symbolic Name

The M that begins the delivery agent definition command is immediately followed, with no intervening whitespace, by the name of the delivery agent. Note that the name is symbolic and is used only internally by sendmail. The name may contain no whitespace, and, if it is quoted, the quotation marks are interpreted as part of its name. In the following, only the first is a good symbolic name:

Mlocal                      <- name is "local", good
M local                     <- error: "name required for mailer"
Mmy mailer                  <- error: "mailer my: `=' expected"
M"mymailer"                 <- quotation marks wrongly retained

Although the symbolic name can contain any character other than a space or a comma, only letters, digits, dashes, and underscore characters are recommended:

Mprog-mailer            <- name is "prog-mailer", good
Mprog_mailer            <- name is "prog_mailer", good
Mmymailer[];            <- name contains a "[];", avoid such characters

The symbolic name is not case-sensitive; that is, local, Local, and LOCAL are all identical.

Note that if two delivery agents have the same name, all the equates for the second definition replace those for the first. Therefore the last definition for a particular symbolic name is the one that is used.

The cumulative result of all delivery agent declarations can be seen by using the -d0.15 debugging switch (see Section 37.5.4, -d0.15) or by using the =M rule-testing command (see Section 38.4.2, "Show Delivery Agents with =M").

30.2.1 Required Symbolic Names

Prior to V8.1, two delivery agent symbolic names had to be defined in every configuration file: local The symbolic name of the program that handles delivery on the local machine (usually /bin/mail). prog The symbolic name of the program that executes other programs for delivery (usually the /bin/sh shell).

Beginning with V8.1, only the local delivery agent is required. If a required definition is missing, sendmail prints one of the following warning messages but continues to run:

No prog mailer defined.
No local mailer defined.

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