Apparently some Windows Phone 7 smartphone users have been experiencing problems with data usage for which Microsoft apparently put the blame on a third party app; however apparently the culprit has now been found and it turns out to be Yahoo! Mail.

According to an article over on Live Side, Rafael Rivera of Within Windows has done some digging and apparently found that Yahoo! Mail was responsible for the abnormal data usage on some Windows Phone 7 handsets, and goes into all the technical jargon.

Furthermore the word is Paul Thurrott of Windows Phone Secrets has heard from Microsoft on this issue and they have now confirmed Yahoo! Mail is causing the problem stating that there is 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.”

Apparently Yahoo! And Microsoft are working on a fix for this problem, which will hopefully be pushed out soon. However for those that are suffering from the issue there is a way to lessen the problem…

To do so you need to click the arrow top right of the Start Screen, select “Setting” from the apps list, then select “email & accounts,” then “Yahoo Mail!,” next click settings under “Download new content,” choose a less frequency setting, then hit the setting under “Download email from,” and choose a shorter time range and change to “the last 7 days.”

Once done hopefully the problem should be lessened for the user until such time as Microsoft can deliver a more permanent fix, and if any of our Windows Phone 7 toting readers try this out, feel free to let us know how you get on.