Some of you may have seen stories about higher than expected data usage for a very small percentage of Windows Phone 7 users being caused by an inefficiency between Windows Phone 7 client and Yahoo! Mail. You may have also seen that these stories mention that there is a separate Exchange ActiveSync (EAS) issue that is impacting a small percentage of users.

Unfortunately, like a game of telephone, many of the stories I've seen are combining these two issues into one, or mentioning both of these issues as if they have equal impact on users. For the record, Yahoo! Mail is not connected to Windows Phone 7 using EAS, and the Windows Phone 7 EAS implementation issue is much smaller. In some of the most egregious cases, some have called this a protocol level bug in EAS. This is untrue — this is a client issue.

We on the Exchange team know that you all work very hard to make sure your Exchange servers are running well, so we wanted to get you some good information (straight from us here at Microsoft) about these issues.

First off; for administrators, there's no need for any changes to your Exchange servers — the issues here are client-side and thus do not impact your servers nor increase the load on your servers.

That said, we know that many of you work closely with your users and always try to help them out with good support information. If you have users who are contacting you about this issue or may be impacted, there are mitigations available for each of these issues while the Windows Phone 7 team continues to work with Yahoo! on a full software fix that is expected in the near term.

For Windows Phone 7 EAS issue, users might see increased data usage when a message is "stuck" in their outbox. A user might encounter this state if they send email to an invalid email address or if they send a message that's larger than the allowed message size (server side policy) from their phone. In these cases, users can go to their Outbox folder and delete the stuck message and the phone's data use will return to normal. Below are the steps a user can take to see if there is a message stuck in their outbox and how to delete it.

Note: This impacts only a very small percentage of Windows Phone 7 users and does not impact EAS users on other phone platforms.

--> The rest is on the Exchange Team Blog :