I agree that the problem recently has been worse than ever. I am using Outlook 2010. It had gotten to the point that I had to change my Internet E-mail Settings on the Advanced tab by un-checking the box that says, "Leave a copy of messages on the server." That fixed the problem, but it is a little inconvenient in that I can no longer see my emails with my cellphone after they are downloaded to Outlook.
I agree...yesterday I had one of my email accounts get hit four times. Infuriating!!!! I try to clean up my AOL account since that's where they are coming from. But if I empty out my AOL account then everything is removed from my cell phone. I'm so tired of this! I've called tech support and had them try to help...hours on the phone and nothing changes. I'm told that since there aren't duplicates with my gmail account (also goes to Outlook) or my cell phone, it is a Microsoft issue. My husband has the same issue and he has spent well over 18 hours on the phone with Microsoft. There's something weird since it NEVER happened when Verizon owned the process.