Various people have commented on issues they’ve had whilst setting up new PCs, especially after the upgrade to Windows 8.1 Preview. The upgrade process is a lot like a reinstall which happens to remember a bunch of settings, and one of the side effects is that it sets up the Mail (and associated Calendar) client as if it was a new PC connecting to your mailbox.
Now, one gotcha you might not be aware of is that Exchange Server can impose a limitation on how many ActiveSync devices are connected – it’s part of the numerous controls IT departments could place on synchronising with mobile devices, such as not allowing certain types of device (eg inherently insecure Android phones) to connect and sync, or by forcing a certain password policy on the phone so it locks when not used for a while.
Windows 8 and 8.1’s inbuilt Mail client uses the ActiveSync protocol to connect to the server, rather than the “Outlook Anywhere” method that the regular Outlook mail client uses. This means that if you reinstall/upgrade your Win8 PC, it could start to chalk off entries on the list of ActiveSync clients associated with your mailbox – and if you think how many phones you might have had in recent years, that number may be close to the limit. You may receive a notification email that there was an “error with your new mobile phone partnership” – strange stuff given than you may be just installing Windows…
Selectively delete some WindowsMail (or old phone) entries that haven’t synched for a while – they’re presumably old and dead. If in any doubt, select a device and click on Details to see the OS type and name of the machine, amongst others.