Urgentblocklimit, normalblocklimit, nonurgentblocklimit, secondclassblocklimit Channel Options

Message size affecting priority
Note that as of the 8.0 release, these size-based priority override channel option effects are nullified if the MT-PRIORITY SMTP extension has been used to set an explicit priority value.

The,  ,   and   channel options may be used to instruct the MTA to downgrade the priority of messages based on size. These options all require a single integer argument specifying the message size, in MTA blocks, at which to perform the priority downgrading. An MTA block is normally 1024 bytes; this can be changed with the   MTA option. This effective priority, in turn, affects the Job Controller&#x27;s scheduling of delivery attempts, higher priority messages normally being attempted before lower priority messages, or see the   Job Controller  options for further control over the scheduling of even initial message delivery attempts, or the    channel options for further control over the scheduling of additional delivery attempts, as well as the   channel options for further control over the "timing out" (bouncing) of undelivered messages.

The  channel option instructs the MTA to downgrade messages larger than the specified size to normal priority. The  channel option instructs the MTA to downgrade messages larger than the specified size to nonurgent priority. The  channel option instructs the MTA to downgrade messages larger than the specified size to second-class priority. Finally, the  instructs the MTA to downgrade messages larger than the specified size to third-class priority.

Note: Both second-class and third-class are nonstandard priority values.

See also:
 * block_size MTA Option
 * Job Controller priority-based processing
 * Size limits on messages channel options
 * Processing control and job submission channel options
 * Channel options
 * mtpriority_policy MTA Option