Semantics of Rewriting Rule Sets

Five rewriting sets have specific semantics, as shown in Figure 3-2.

Figure 3-2 Rewriting Set Semantics

Rule set 3 is applied by sendmail before sendmail handles any name. Rule set 3 should turn the name into a form, with the basic syntax:

local-part@host-domain-spec

If no @ is specified, then the host-domain-spec may be appended from the sender name (if the C flag is set in the mailer definition corresponding to the sending mailer).

Rule set 0 is applied after rule set 3 to names that will actually specify recipients. It must resolve to a mailer, host, user triple. The mailer must be defined in the mailer definitions from the configuration file. The host is defined into the $h macro for use in the argument expansion of the specified mailer; the user is defined into $u.

Rule set 1 is applied to all From: recipient names, and rule set 2 is applied to all To: and Cc: lines. Then the rule sets specified in the mailer definition line (and R=) are applied. This process is done many times for one message, depending on how many mailers the message is routed to by rule set 0.

Rule set 4 is applied last to all names in the message. It is typically used to translate internal to external form.