The $g macro is identical to $f except that it undergoes additional rule-set processing to translate it into a full return address. During delivery the sender's address is processed by the canonify rule set 3, the rule set 1, and the final rule set 4, and then placed into $f. That rewritten address is further processed by the canonify rule set 3 and rule set 1 again, then rewritten by the rule set specified in the S= equate of the delivery agent. Finally, it is rewritten by the final rule set 4, and the result is placed into $g.

$g holds the official return address for the sender. As such, it should be used in the From: and Return-Path: header definitions.

The S= equate for each delivery agent must perform all necessary translations to produce a value for $g that is correct. Because the form of a correct return address varies depending on the delivery agent, other rule sets should generally not be used for this translation.

Ordinarily, RFC2822 comments (Section 25.3.4) are restored when $g is used in headers. To omit those comments (perhaps for security reasons), you can use the F=c delivery agent flag (F=c).

$g is transient. If it is defined in the configuration file or in the command line, that definition can be ignored by sendmail. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&g, not $g).