Confirmed: Yahoo! Mail is the data leak culprit in Windows Phone

Update: Microsoft has confirmed this is the issue. See my newer post for more info.

The reason Rafael is so valuable is because he can do stuff like this: Prove that Yahoo! Mail is the reason some people are experiencing massive data usage issues on Windows Phone.

Sniffing out IMAP packets to and from a Windows Phone isn’t as straight forward as it sounds. Microsoft’s IMAP4 implementation is very aware of the STARTTLS extension emitted by IMAP servers and switches to encrypted communication as soon as its detected, kinking the sniffing operation. (Worse, there’s no official UI for forcing clear-text communication.) To workaround this, I wrote a quick nodejs script to strip IMAP connections of the STARTTLS bit and passed them on to their destination.

What I discovered was shocking, although not surprising. Yahoo’s IMAP server ( does not respond to FETCH requests correctly.

Yahoo is sending ~25 times as much data as it needs to. (This can also be read as: Your phone is downloading ~25 times as much data as it normally would, had you sided with another email provider.)

This doesn’t mean that there aren’t other issues in Windows Phone that are causing data to leak. For example, I believe there to be a bug in the OS that causes Wi-Fi to disconnect under certain conditions, unnecessarily firing up extra 3G usage routinely. But I’m guessing this is a big part of the problem, the major part of it.

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24 Responses to Confirmed: Yahoo! Mail is the data leak culprit in Windows Phone

  1. jonahu says:

    Must be something else causing my spike in data usage as I don’t use Yahoo Mail for wp7. The Wi-Fi disconnect issue seems more applicable in my case.

  2. Rains says:

    Something of intrest on this line…We purchased two WP7 on November 26, 2010.
    Yesterday, I made a trip to the AT&T store because we could only connect on line when using WiFi. It turns out that BOTH of the phones had to have new SIM cards.
    I don’t understand this! Any other problems like this out there…

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  4. blkballoon925 says:

    So this is the third-party issue that Microsoft determined, but couldn’t tell us? Must be that Yahoo!/Bing deal that is keeping them quiet. Why else would they be afraid to admit it is a competitor’s (Hotmail and Bing, after all are competitors to Yahoo! Mail and Search) service that is causing a big part of the problem.

    • nicholas1029 says:

      I think it was a good-neighbor type move Microsoft made. Rather than outright criticizing Yahoo, they tried to keep it quiet. Stuff like this has the potential to hurt an already struggling company. However, now that the cat is out of the bag, it made no difference if Microsoft confirmed it. Microsoft isn’t all evil ya know. ;-)

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  8. Mike Cerm says:

    YES! This is totally Yahoo’s fault, and not Microsoft’s, because this exact thing happens in WebOS as well. My brother uses a 1GB per month on his Palm Pre because he has a legacy Yahoo mail account on there. (He’s been aware of the problem for a while, but Sprint isn’t nearly as stingy with data, so he just leaves it on there.)

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  16. jahman7 says:

    Glad to see this (and other non confirmed issues) is the problem. I would be even more glad to see it fixed… Till then, I have to micromanage my data usage, and overall, I use about 40-100MB per month by simply turning off data usage when I don’t need it. Like you, Paul, most if not all of my connecting to the cloud/web happens over WiFi. I only turn on my data usage on those rare events that I need navigation or random info when not connected to WiFi. It would be nice to not have to worry about turning it off because I do like to get notifications especially when I’m mobile. However, I also do this to conserve battery life.

    Is this device truly mobile if it is not reliably predictable in what it does when mobile? I suppose because it’s pocketable, the answer is yes… but not by my standards.

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