The MTA tracks messages as they arrive, queues them in memory in the "in progress" queue, and stores them in the gwinprog directory until they have been processed.You can control the amount of memory the MTA uses to queue messages.
By default, the MTA allocates an "in progress" queue size of 32 entries for messages, which uses approximates 60 KB of memory. Use the /queuebasesize switch in the MTA startup file to control the initial size of the MTA "in progress" queue.
Set /queuebasesize to a higher number if you want the MTA to be able to hold more message entries in memory. Set /queuebasesize to a lower number to conserve memory.
By default, the MTA allows its "in progress" queue to expand to as many as 65,000 entries. Use the /queuemaxsize switch in the MTA startup file to control the maximum size of the MTA "in progress" queue.
Set /queuemaxsize to a higher number if memory is plentiful. Set /queuemaxsize to a lower number to conserve memory for other purposes. Entries for arriving messages that cannot be held in memory are written to the gwinprog directory and retrieved from there as messages depart from the "in progress" queue.
By default, the MTA increases its "in progress" queue in increments of 32 entries until the /queuemaxsize setting is reached. Use the /queuesizeincrement switch in the MTA startup file to control the number of entries the MTA adds to its "in progress" queue each time.
Set /queuesizeincrement to a higher number so the MTA adds more entries each time the queue needs to grow. Set /queuesizeincrement to a lower number so the MTA adds fewer entries each time the queue needs to grow.
The "in progress" queue also shrinks according to the /queuesizeincrement setting when fewer entries are required to handle current message traffic.