I have a user who sent an email in Outlook (using the zimbra connector) which ended up being sent multiple times.

The mail was still in his Outlook outbox and was being sent over and over again. It stopped sending when he deleted it from the outbox in outlook.

The user also uses zimbra mobile which would have been syncing and so on at the same time, but the email in question was done solely in Outlook.

Any ideas as to why? And more importantly how I make it not happen again.