For some sites, processing all messages, of whatever sort, as quickly as possible is the major goal, and issues of message size or message priority are not a concern.

Other sites can want to treat messages over some site-specified size as deserving of lower priority or delayed processing, as compared with messages of a more "normal" size.

PMDF by default pays attention to message priority when processing more than one message (as for a PMDF periodic delivery job) and will automatically try to send messages of greater priority before trying to send messages of lower priority. To get generally different handling of messages of differing priority, the nonurgentqueue, normalqueue, and urgentqueue channel keywords can be used to cause messages of differing priority to be processed in different processing queues; see Section 2.3.4.18. Such different processing queues might have different resources devoted to them, for instance, different job limits as to how many simultaneous jobs can run at once; or a processing queue used for processing non-urgent messages might be set up to run only at off-hours.

PMDF can be configured to treat messages over site-specified sizes as having an effectively lower processing priority via the nonurgentblocklimit, normalblocklimit, and urgentblocklimit channel keywords, or the NON_URGENT_BLOCK_LIMIT, NORMAL_BLOCK_LIMIT, and URGENT_BLOCK_LIMIT PMDF options; see Section 2.3.4.10 or Section 7.3.5, respectively. In conjunction with differential priority handling, as described above, this can provide for differential handling of messages of varying sizes.