We have a user who has these devices connected to our MX server;

iPhone 

iPad

Desktop Win 7 Pro, Outlook 2010

Laptop Win7 Pro, Outlook 2013

He will open an e-mail look at it, then delete. It then goes into the deleted items folder and duplicates as one read and one unread. We have not been able to figure out why this is happening. We have tried disconnecting all devices and reconnecting them, no joy. Tried recreating the .ost, no joy. Tried recreating user profile, no joy.

At one point we disconnected his laptop because he was getting a new one and it stopped doing it for the most part, still happened but not very often. Then we brought the new laptop online and it returned with a vengence. So we disconnected all devices and reconnected all devices except his desktop. He ran the weekend with no duplicates, Monday when we reconnected the desktop it came back strong.

It seems to be tied to the cached mode and Offline use. I did a complete uninstall/re-install and turned off cached mode for the re-up and had zero duplicates. A few days later I renamed the .ost and started Outlook and it immediately started popping dups on the other machine. I cancelled the build went and turned off the offline files option in outlook and restarted. No dups. I don't want to have this user operating without cached mode due to it being slower and having to wait if he loses the network briefly. Any ideas?

Hi,

Which device does he use to open and delete the email?

According to your description, my understand is that you use multiple protocol in different devices to deal with emails simultaneously. right?

I recommend that disconnect all the devices and use OWA to check if there is the same issue.

If no, you need to check if the settings on the different devices is correct.

Hope this helps!

Thanks.

"So we disconnected all devices and reconnected all devices except his desktop. He ran the weekend with no duplicates, Monday when we reconnected the desktop it came back strong."

"It seems to be tied to the cached mode and Offline use. I did a complete uninstall/re-install and turned off cached mode for the re-up and had zero duplicates. A few days later I renamed the .ost and started Outlook and it immediately started popping dups on the other machine. I cancelled the build went and turned off the offline files option in outlook and restarted. No dups."

However now it seems he has started getting the duplicates again even though he is Not running in cached mode and is not downloading shared folders. 

New information: This is ONLY happening with external emails, emails outside the domain, operating in cached mode