Exchange 2013 stops processing emails about every 1.5 to 2 days
Event 6005: SmtpReceiveProtocolLogs: Failed to flush logging requests fast enough (maximum requests of 50000); was forced to flush synchronously. This indicates high disk latency or issues with thread starvation and indicates a performance problem.
Along with A message with the Internal Message ID XXX was rejected by the remote server. This message will be deferred and retried because it was marked for retry if rejected. Other messages may also have encountered this error.
At first I thought it was a drives space issues but the last hang was with 10 gig free space and that is double of where it used to be.
If I go to the Cloud spam filter service and run a test email I get this: Unable to set DATA: 452-4.3.1 Insufficient system resources