sendmail, 4th Edition

The P Configuration Command

The P configuration command must begin a line. This command is composed of four parts:

Pstring=value

The string is text, such as special-delivery. Everything between the P and the = (including any whitespace) is taken as is for string. The value is evaluated as a signed integer and can be decimal, octal (with a leading 0), or hexadecimal (with a leading 0x).

Although you can define any string you choose, only five have any universal meaning. Those five usually appear in sendmail.cf files like this:

Pspecial-delivery=100
Pfirst-class=0
Plist=-30
Pjunk=-60
Pbulk=-200

You can, of course, define your own precedence strings for internal mail, but they will be ignored (evaluate to 0) by all outside sendmail programs.

The classes junk and bulk are also recognized by many other programs. Newer versions of the vacation(1) program, for example, silently skip replying to messages that have a Precedence: header line of junk or bulk.

As a general rule, special-delivery is rarely used. Most mail has a class of first-class. Mailing lists should always have a class of list or bulk.

Because your local sendmail.cf file is where values are given to these class names, you are free to modify those values locally. The values affect only the delivery at your site.

Old versions of sendmail didn’t return errors on messages with a negative precedence. V8 sendmail does but omits the message body.