Windows Phone data problems traced to Yahoo! mail app (we knew that)

within-windowsA small percentage of Windows Phone users (man, that must be a REALLY small number) apparently have been seeing abnormal data usage on their Windows Phones, and today our pal Rafael Rivera from Within Windows posted on some experiments he did which showed that the Yahoo! Mail app indeed did seem to be generating a lot more data usage than necessary or desirable.

Then Paul Thurrott (who co-authored Windows 7 Secrets with Rivera) rattled enough feathers in Redmond to get them to admit that Yahoo! Mail was indeed at fault, and even to admit to some other sins as well.

Of course Mary Jo Foley pointed to reports that Yahoo! Mail was the culprit weeks ago (although we don’t think she wrote a “quick nodejs script to strip IMAP connections of the STARTTLS bit”, like Rafael did).  In her post on the problem dated January 21, she laid out the problem and noted the reports of the Yahoo Mail app as the culprit:

Microsoft officials said this week that the excessive data uploading experienced by some WP7 users is due to a third-party application. Microsoft declined to name the company or application, but did say company officials were working with the company in question to fix the application. Microsoft may possibly provide a workaround, officials said. I’ve seen two credible reports that are pointing fingers at Yahoo Mail as the possible culprit. I didn’t receive a response from Yahoo when I asked, and Microsoft execs also declined to comment specifically on Yahoo Mail being possibly at fault.

So it isn’t really news that Yahoo Mail is known to cause issues with Windows Phone data usage.  But even with today’s admission, questions still linger.  Is the Yahoo! Mail app the only culprit?  Why was the malformed app allowed in the Marketplace in the first place?  And why hasn’t Microsoft (and Yahoo!, for that matter) been more forthcoming about the whole situation?