> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
   > [[[ whether defending the US Constitution against all enemies,     ]]]
   > [[[ foreign or domestic, requires you to follow Snowden's example. ]]]


   > Yes, that is right.

   > Referring to any external elements from HTML in an email
   > exposes the user to various forms of mistreatment.
   > Security in an MUA includes protecting the user from all that.



   > It's often not "people".  Many companies systematically use this
   > security hole to track users.  I am very glad that nobody can
   > tell whether I have read a message -- because I do it in Emacs.

A word of warning should be added.

There are configuration in emacs, for which  such a tracking is
successful.

For example using gnus the setting

(setq gnus-blocked-images nil)



Explanation.

I was not aware of this sort of tracking software and found out that
google's chrome browser has dozen of extension for email tracking, some
of them commercial. I downloaded and tried all of them, (well the ones
which did not require a payment). I then sent message to my own account
(my university switched to a google account which I access via imap).

Indeed with the above setting one extension successfully discovered that
I read an email with gnus/emacs.