Values for the Precedence:
field may be defined using the
P control line. The syntax of this field is:
Pname=num
When the name is found in a Precedence:
field,
the message class is set to num. Higher numbers mean
higher precedence. Numbers less than zero have the special property
that if an error occurs during processing the body of the message
will not be returned; this is expected to be used for ``bulk''
mail such as through mailing lists. The default precedence is zero.
For example, our list of precedences is:
Pfirst-class=0 Pspecial-delivery=100 Plist=-30 Pbulk=-60 Pjunk=-100People writing mailing list exploders are encouraged to use
Precedence: list
. Older versions of sendmail
(which discarded all error returns for negative precedences)
did not recognize this name, giving it a default precedence of
zero. This allows list maintainers to see error returns on both
old and new versions of sendmail.