for email there exists no update-alternatives directory. You may take a look at the faq at:couldnt find anything in update-alternatives re evolution kmail or email
http://www.jwsdot.com/debian/faq.html#q9this faq states how to set the http(s) handler. For mailto handlers, it should be quite similar.
-- GPG messages preferred. | .''`. ** Debian GNU/Linux ** Alexander Sack | : :' : The universal asac@jwsdot.com | `. `' Operating System http://www.jwsdot.com/ | `- http://www.debian.org/