This is not 100% related, but I like to play around the with
the Message-ID, specifically I randomize the domain and then
the user agent.  Sometimes I don't want to reveal my "home"
domain.

This works with many email providers, but there are some
forwarding or bulk services that rewrite the Message ID.
Naughty of them.

My code is below.  Please realize I'm not exactly the No. 1
elisp coder --- but it does work in my environment.

-- 
Bob Newell
Honolulu, Hawai`i

- Via GNU/Linux/Emacs/Gnus/BBDB