Microsoft officially confirms that Yahoo is the cause of the Windows Phone 7 data issue

Surprise, surprise! There’s no Windows Phone 7 data usage bug and Yahoo is the third-party service to blame according to Microsoft who officially confirmed what I have been saying all along. So, what else is there to say? Well, maybe folks should do some research before posting “Breaking News” stories about deal breaking Windows Phone 7 OS bugs. The Yahoo Mail data issue has been reported several times in public forums ever since the platform was launched last year….Microsoft is also going to fix a totally unrelated Exchange EAS issue. Check out Microsoft’s full statement after the break:

We have determined that an inefficiency exists in the synchronization of email between the Windows Phone Mail client and Yahoo! Mail.

This inefficiency can result in larger than expected data usage for a very small percentage of users.

Microsoft and Yahoo! have worked together to identify a fix, which will be rolled out in the coming weeks.
In the meantime, customers can mitigate this issue by following these steps:
On the Start screen of Windows Phone 7, click on the arrow at the top right
Choose “Settings” from the app list
Choose “email & accounts”
Choose “Yahoo! Mail”
Click on the setting under “Download new content”
Select a less frequent setting. If you are using the default setting (every 2 hours), change this setting to ‘manually’
Click on the setting under “Download email from”
Select a shorter time range. If you are using the default setting (the last 2 weeks), change this setting to ‘the last 7 days’

Microsoft has also identified an issue with our Exchange ActiveSync [EAS] email synchronization protocol that may affect a very small percentage of users

This issue can be caused by email that exceeds the mail server email size setting or is sent to an invalid email address
This issue can potentially affect email services that utilize the EAS protocol – Outlook and Gmail for example
The immediate mitigation is for users to delete mail that appears “stuck” in the outbox
This is currently scheduled to be fixed in a near-term end user update from Microsoft

Thanks for the tip Josh