Why do some messages appear multiple times in a users inbox?
There are several ways this can occur. Basically there is a known ‘issue’ with smtp where a timeout/failure during the ‘data’ stage after the ‘dot’ is sent by the sender, can result in the receiving system thinking it’s got the message while the sending system thinks it failed to send it so retries. Usually this occurs due to something slightly odd going on like a virus scanner interposed in the channel which is causing a multi minute delay while it accepts the message from one end but doesn’t send it on to the other end. So, first, you need to identify where the duplication occurred, in the surgemail logs find the message id in question and you will see if it was received multiple times or not. Then go backwards to the source till you know where the duplication is occurring, then on both systems in question (the sender or mail client and receiving mail server) look for virus scanners and smart spam filters that might have caused an issue. And increase any timeouts you can see, in surg
