Recently we installed Windows 8 on our Dell E6500 and the installment smoothly however we ran into an issue with the default mail app synching to our Office 365 email account. This was particularly confusing since setting up Office 365 email in the Windows 8 Mail app has never been an issue. As it turns out, the mail app is treated as a mobile device and there is a limit of ten different devices that an Office 365 Account is allowed to synchronize with. In order to fix this we had to login to the Office 365 admin panel and remove the unused devices.
How to manage Office 365 Mobile devices
The first step is to log into your Office 365 email account and hit “options” in the top right corner.
Next, While in options hit Phone on the left hand side of the screen
Finally, highlight the devices you would like to remove to free up some space and hit the delete button at the top.
After removing the additional devices you should be able to add the Windows 8 Mail app without issue.