I know there are multiple spool folders but I notice every time when 500+ emails are in all spool folders that the systems are having trouble functioning quickly, though I have my spool running on 15k raid 10 disks, I/O must be fast enough.

My server is also the incoming gateway for a number of customers. At this moment there is an internet provider with a long disruption of its services

So e-mail is piling up in the spool folders

What if there were not only spool folders no. 1 to 10 but also delayed spool folders where mail is moved to when mail sits longer than x retry timers in the spool.