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Yahoo! mail header format

The Yahoo! Web Mail header format has changed over time, but currently includes the sender's IP address, a domain key signature, and some other helpful information.


DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;

Here is a sample mail header. Note that the 'date' field will change from (PDT) to (PST) depending on the status of daylight savings time in California, USA. The sender's IP address is represented as a.b.c.d in the example below.

Mail Header

Received: from [a.b.c.d] by via HTTP; Sat, 14 Feb 2009 05:42:03 PST
X-Mailer: YahooMailWebService/
Date: Sat, 14 Feb 2009 05:42:03 -0800 (PST)
From: Sender Name <>
Subject: Test Message
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Message-ID: <>

Message IDs

The Message-ID header in yahoo emails is a good identifier for the device that sent the message. Below are some samples:

Sent via Yahoo!® Mail for Android application on Android (Jelly Bean):

Message-ID: <>

Sent via Yahoo Webmail from Chrome:

Message-ID: <>

Sent via Android browser on via mobile webmail interface:

Message-ID: <>

Sent via Android email application configured for SMTP (jelly bean):

Message-ID: <>

Sent via iPod (IOS 5.0.1)

Message-ID: <>

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