The urgentblocklimit, normalblocklimit, and nonurgentblocklimit keywords may be used to downgrade the priority of messages based on size. This priority, in turn, may affect whether the message is processed immediately, or whether it is left to wait for processing until the next periodic job runs.
The urgentblocklimit keyword instructs IMTA to downgrade messages larger than the specified size to normal priority. The normalblocklimit keyword instructs IMTA to downgrade messages larger than the specified size to nonurgent priority. The nonurgentblocklimit keyword instructs IMTA to downgrade messages larger than the specified size to lower than nonurgent priority (second class priority), meaning that the messages always wait for the next periodic job for further processing.