I've been trying to track down, why one of my users stays a number of emails yesterday were not delivered. So looking in the log files, | can see that everything was OK, apart from one strange thing.

All lines in zimbra.log are are repeated twice. Dose this mean all emails moving around are being done twice or just logged twice?

If the system is trying to deliver all messages twice, could this sometimes cause the system to reject both and not deliver the message?