Stewart Dean schrieb:
When this happens with sendmail, it can be that the queue handler doesn't finish before a new queue handler is kicked off, so each successive queue handler/runner ends up sending the same mail. Background: sendmail, and perhaps postfix, is configured to a) toss stuff it can't handle right away into the queue and then, every so often (interval to be set by admin), it burps the queue. If the interval is too short, the previous queue handler/runner doesn't complete before a new one is invoked and gets it list of things to mail...with the same email on both queue handler/runners incarnations to do list...........
Postfix can cause duplicate messages in certain circumstances if and only if messages are delivered and the delivery is not reported to postfix, or in adverse conditions for messages to multiple recipients. It will log this however, and Postfix's queue runner isn't stupid (and there's only one at a time).
So please don't guess, randomly pointing naked fingers at dressed MTAs :-)