You may not have the correct settings, depending on the email address being used (similar thread and link here, if you are using the windows 8 mail app). The Windows 8 mail app may well have problems that need to be addressed in future, as I found it to have synching problems with particular emails for no good reason. It wouldnt show them. If your settings are correct, whether you are using Windows Live Mail or the windows 8 mail app, you could try re-installing either, to the latest versions if possible, see if that makes any difference. I would probably try to make sure I did not have more than one mail client running also, eg if always using Windows Live Mail, there is no need for the windows mail application to also be running.Turn it off or uninstall it.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been