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.