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Today our spool got backed up. The status for most of the messages was "Local Delivery". Our server had plenty of memory and CPU available but during the peak time of the day SmarterMail could not deliver fast enough. We did not have any attacks, spammers, etc. during this period. Our users had ~1hr delivery delay.
Does anyone have any tips to isolate what is causing the delivery problem? During the spool backup the messages seem to process periodically and it appears that they are stuck in a process.