X-Mozilla-Keys (offline messages) in forwarded message (as an attachment)
When Thunderbird (TorBirdy 0.2.1) downloads and saves an email locally it at adds X-Mozilla-Keys, if the user forwards those email as an attachment the X-Mozilla-Keys are still in the email (resp *.eml-file) (what makes perfectly sense for signed emails)
excerpt from the received email's source code:
--------------
Content-Type: message/rfc822;
name="test.eml"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="test.eml"
X-Mozilla-Keys:
To:
And thereby it leaks the users email agent.