I am a big fan of the Nokia Lumia devices. These Windows 7.5 (Mango) devices have a very tight integration with services such as our own cloud based Microsoft Exchange mailboxes and Microsoft SkyDrive accounts.
We have recently identified an issue with Windows 7.5 that does not seem to be well identified or discussed that we have replicated on multiple Lumia's with entirely different Exchange servers. These issues relate to synchronisation failures of read / unread status and deletion of email from the server after deletion if email from the handset.
Our testing has been reasonably cursory (we have not tested calendar sync for example) but these are our findings:
Download New Content “As Items Arrive”
When the phone is configured to synchronise ‘as items arrive’, new emails are correctly ‘pushed’ to the device and so new inbound emails are delivered to both the mailbox and handset in a fast and timely manner. Unfortunately, it also appears that using the same ‘as items arrive’ setup, some things (such as the fact that an email has been marked as read or unread) do not properly synchronise back to the server. Forcing the phone to synchronise manually (by using the sync button, not by changing the configuration) does synchronise these more subtle changes with the server.
Download New Content “Every 15 Minutes”
When the phone is configured to synchronise ‘every 15 minutes’, new emails will not be delivered to the device as quickly, but will appear on the device at the next scheduled time, theoretically at an average of 7.5 minutes later. Keeping the phone in this state appears to make the device do a ‘full’ synchronisation every 15 minutes and so a full mailbox update is performed, including the read / unread information.
So, if you are keen to have emails delivered quickly, you should configure the phone to download content ‘as items arrive’ but remember to do an occasional manual sync to update read / unread data back to the server.
If you are keen to have a better synchronised mailbox and are prepared to wait a few minutes to see inbound email, you should configure the phone to download content ‘every 15 minutes'.
These synchronisation options are available in: Settings > Email & Accounts > Outlook (or whatever Exchange account you want to edit). Look for the ‘Download New Content’ option which appears near the top of this screen.