> Can you clarify this a bit? I don't really understand the problem - I have an Exchange server synced on my iPhone and there are no problems.

The native email app does not sync mails that are being filtered into folders properly. Or let's say: it sometimes does it, sometimes it does not. I just lost any trust into it and drag down every folder to be sure that there isn't a new mail in there. It's a pain. I asked around on the forums and reddit and even though the issue is not new, nobody could help me out. Some pointed out that it surely is an issue with the server but it works flawlessly with the Windows Phone and Android.