On Apple OSX the following issue is very bad to solve:

Crashed Thread:        23  -[DeliveryQueue _deliverQueuedMessages:]  Dispatch queue: NSOperationQueue 0x7fcf5eb248f0 :: NSOperation 0x7fcf62396ec0 (QOS: UTILITY)

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Encoding a malformed address (unbalanced quote or parenthesis), bad things may be about to happen.
"XYZ,'
abort() called
terminating with uncaught exception of type NSException

There are some articles how to potentially solve it with deleting settings of mail etc. but there is another solution:

– Turn the system to offline mode (turn of WiFi etc.)
– Open Mail
– Search for the email with malformated content
– delete the email
– close Mail
– Turn the system back to online mode
– start Mail again

–> Done

Hope that helped