When sendmail processes the messages in its
queue, it sorts them by priority.* 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:
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 (?§25.10 on page 1148) in the sendmail.cf file.
z
Value given the ClassFactor option (?§24.9.15 on page 984) 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.
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