Albert -- The page you mention (<a href="http://www.jwz.org/doc/threading.html">http://www.jwz.org/doc/threading.html</a>) says "I'm told this algorithm is also used in the
<a href="http://www.gnome.org/gnome-office/evolution.shtml">Evolution</a>
and <a href="http://www.balsa.net/">Balsa</a> mail readers.
"<br>