Not all messages need to be treated equally. When sendmail processes the messages in its queue, it sorts them by priority.^[56] The priority that is given to a message is calculated once, when it is first created, and adjusted (incremented or decremented) each time it is processed in the queue. You can think of priority as a cost, where mail with the lowest priority number (lowest cost) is handled first. The formula for the initial calculation is:

^[56] See the QueueSortOrder option, QueueSortOrder, for alternative ways to sort.

priority = nbytes - (class * z) + (recipients * y)

The items in this calculation are as follows:

priority

Priority of the message when it was first created.

nbytes

Number of bytes in the total message, including the header and body of the message.

class

Value given to a message by the Precedence: line in the header of the message. The string following the Precedence: is usually either first-class, special-delivery, junk, bulk, or list. That string is converted to a numeric value determined by the P command (Section 25.10) in the sendmail.cf file.

z

Value given the ClassFactor option (ClassFactor) and a weighting factor to adjust the relative importance of the class.

recipients

Number of recipients to whom the message is addressed. This number is counted after all alias expansion.

y

Value given this RecipientFactor option and weighting factor to adjust the relative importance of the number of recipients.

The forms of the RecipientFactor option are as follows:

O RecipientFactor=factor                  configuration file (V8.7 and later) 
-ORecipientFactor=factor                  command line (V8.7 and later) 
define(`confWORK_RECIPIENT_FACTOR',factor)    mc configuration (V8.7 and later) 
Oyfactor                                  configuration file (deprecated) 
-oyfactor                                 command line (deprecated) 

The argument factor is of type numeric. If that argument is missing, the default value is zero. If the entire RecipientFactor option is missing, the default value is 30000 (thirty thousand). The default for the mc technique is to omit this option.

The RecipientFactor option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.