Microsoft confirms Yahoo as phantom data culprit

In the continued investigation of the mysterious Windows Phone 7 phantom data usage, Rafael Rivera has managed to beat Microsoft to the punch and proclaim Yahoo email as the culprit. The mysterious 'phantom' data appeared earlier this month, using excess bandwidth on a users phone, leaving some customers with a higher than normal phone bill.

As Rafael from Withinwindows.com discovered, Yahoo's IMAP server is the root cause of the issue. As he investigated into the matter even further, he discovered that Yahoo's mail response server was sending approximately 25 times the amount of data a regular IMAP server would.

Although the communications aren't sending large chunks of data, times the number of emails you currently have in your Yahoo account, and you can easily rack up the extra few megabytes per sync.

A normal "fetch" response (AIM):

* 1 FETCH (UID 258 BODY[HEADER.FIELDS (MESSAGE-ID)] {81}
Message-Id: [contoso194089-0-1475496219-3-11262342655328369@CONTOSO.COM]
FLAGS (XAOL-RECEIVED XAOL-GOOD XAOL-GOODCHECK-DONE XAOL-CERTIFIED-MAIL XAOL-BILLPAY-MAIL $hasEmbedded))
...
OK FETCH completed

Now, Yahoo's "fetch" response:

X-YMAIL-UMID: 1_1231_AH9SAiosajdifsLGYp8
Delivered-To: rafael@withinwindows.com
Received: by 0.0.0.0 with SMTP id b14cs36932vcd;
        Wed, 24 Nov 2010 09:48:20 -0800 (PST)
[snipped]
Received-SPF: pass (google.com: domain of bxp60spbgycisj582h2kt@contoso.com designates 0.0.0.0 as permitted sender) client-ip=0.0.0.0;
DomainKey-Status: good (test mode)
Authentication-Results: mx.contoso.com; spf=pass (contoso.com: domain of bxp60spbgycisj582h2kt@contoso.com designates 0.0.0.0 as permitted sender) smtp.mail=bxp60spbgycisj582h2kt5hjwxuss6f@contoso.com; domainkeys=pass (test mode) header.From=dummy@contoso.com
DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
  s=200505; d=email.contoso.com;
  b=[snipped]+CKirfbuapQiU=;
h=Date:Message-ID:List-Unsubscribe:From:To:Subject:MIME-Version:Reply-To:Content-type;
Date: Wed, 24 Nov 2010 17:48:39 -0000
Message-ID: [bxp60spbgychw1axh2kt.7412145937.3427@MTA915.CONTOSO.COM]
List-Unsubscribe: [mailto:rm-0bxp60spbgychw1axh2kt@EMAIL.CONTOSO.COM]
From: "Contoso" [dummy@EMAIL.CONTOSO.COM]
To: rafael@withinwindows.com
Subject: This is a test message
MIME-Version: 1.0
Reply-To: "Contoso" [dummy@EMAIL.CONTOSO.COM]
Content-type: multipart/alternative; boundary="=bxp60spbgychw1axh2kt5hjwxuss6f"
...
OK FETCH completed

Microsoft has since confirmed Yahoo as the culprit behind the Windows Phone phantom data. It's recommended that you disable data roaming (Settings -> Cellular -> Data Roaming) for the time being.

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