Trend analysis on *Rejected* and *Failed* might be useful in determining potential channel problems.
A sudden jump in the ratio of mtaGroupStoredVolume to mtaGroupStoredMessages could mean that a large junk mail is bouncing around the queues.
A large jump in mtaGroupStoredMessages could indicate unsolicited bulk email is being sent or that delivery is failing for some reason.
If the value of mtaGroupOldestMessageStored is greater than the value used for the undeliverable message notification times (notices channel keyword) this may indicate a message which cannot be processed even by bounce processing. Note that bounces are done nightly so you will want to use mtaGroupOldestMessageStored > (maximum age + 24 hours) as the test.
If mtaGroupLoopsDetected is greater than 0, a mail loop has been detected.