When sendmail processes the messages in its queue, it sorts them by priority and handles those with the lowest priority first.

The priority of a message is calculated once, using the RecipientFactor (RecipientFactor) and ClassFactor (ClassFactor) options, when the message is first created, and it is adjusted, using this RetryFactor option, each time the message is processed in the queue.

Each time a message from the queue fails to be delivered and needs to be requeued, its priority is adjusted. That adjustment is made by adding the value of this RetryFactor option.

The forms of the RetryFactor option are as follows:

O RetryFactor=inc                 configuration file (V8.7 and later) 
-ORetryFactor=inc                 command line (V8.7 and later) 
define(`confWORK_TIME_FACTOR',inc)    mc configuration (V8.7 and later) 
OZinc                             configuration file (deprecated) 
-oZinc                            command line (deprecated) 

The argument inc is of type numeric. If inc is missing, the default value is zero. If the entire RetryFactor option is missing, the value for inc defaults to 90000 (ninety thousand). The default for the mc technique is to omit this option. The increment is performed by adding the value of inc to the previously stored message priority each time that message is queued.

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