I don't know if this will help.
I use Outlook Express instead of Outlook because it allows me to have two E-mail addresses on the same computer without uninstalling and reinstalling the program to view mail for an other address.
I was experiencing that problem (sometimes I had 3 or 4 copies of the same E-mail) I found that my E-mail download was being interrupted by my Anti-Virus when it came to a suspicious message. When I attempted to do a Send/Receive again the server or my client did not recognize that mail had already been downloaded prior to the interruption, and downloaded it again. The tech. at Comcast suggested that I disable my Anti-virus. I reluctantly did and my E-mail finished the download without interruption. The suspicious piece of E-mail was fine but did not have a subject. I later found that I could go to my Mail through my browser whenever the problem arose, and delete any suspicious E-mail, to clear it.
Comcast or Norton has since changed the screening rules and the problem has not occurred for over a year.
I imagine that your E-mails are being sent only once but downloaded more than once. If you have the ability to read your E-mail through the web try it and see if you are being sent duplicates or simply duplicate downloading the same messages.
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