I have an issue on a clients with where outlook 2013 repeatedly downloads all mail left on server each time you open it. The client leaves 5 days of mail on the POP server so he can also download it on his laptop. This has worked for years with Outlook 2007. We recently upgraded both his systems to Office 2013, and now, just one one of the computers, this behavior has started.
It doesn’t re-download it as long as outlook is open, but when you close and open, it will download everything again once. Its like closing it resets whatever flag in outlook tracks whether its downloaded an email already. I've tried a new data file and profile but it hasnt resolved it.