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").