The sendmail program uses the $r sendmail macro ($r) to store the protocol used when sendmail first received a mail message. If the message was received by using SMTP, that protocol is smtp. Otherwise, it is NULL.

The sendmail program uses the $s sendmail macro ($s) to store the full canonical name of the sender's machine.

The sendmail program uses the $_ sendmail macro ($_) to store RFC1413 identd(8) information and IP source-routing information.

When sendmail creates a qf file, it saves the values of the $r, $s, and $_ sendmail macros in lines that begin with $.

The form of the $ line in the qf file looks like this:

$Xvalue
${XXX}value

The $ must begin the line, and the sendmail macro's single-character name (the X) or multicharacter name (the {XXX}) must immediately follow with no intervening space. The sendmail macro's name is followed (again with no intervening space) by the value of the macro.

If value is missing, the value given to the macro is NULL. If the macro name and value are missing, the macro \ is given a value of NULL. If both are present, the macro whose name is specified is given the value specified (value).

There can be multiple $ lines. The sendmail macro names to be stored in the qf file are listed in the $={persistentMacros} class ($={persistentMacros}).