Recently I just started receiving Duplicate E-mail Messages .....
Mail 4.6, Snow Leopard 10.6.8, MacPro 4.1
For quite some time I was not receiving Duplicate Messages, but now it's happening again. Only a few days ago, I deleted the Plist, but obviously that did not help.
I suddenly got duplicates in my inbox a couple of days ago – not all of them, only emails received in the last month were duplicated. Switching off then on again made no difference, this morning they were still there, but suddenly they disappeared. They went as mysteriously as they arrived!
Maybe just leave your machine to sort itself out?
If you are using a recent version of OS X the library folder is hidden, The Apple Mail plist is on one of the subfolders. See here for directions on how to unhide the Library folder. The Mail plist is in the Preferences folder.
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