Gmail will offer to automatically unsubscribe from a mailing list1, so why can't mutt?

Gmail parses the List-Unsubscribe header looking for a mailto URL, so it should be quite possible to knock up something similar for mutt.

A typical List-Unsubscribe looks like:

List-Unsubscribe:
    <http://zgp.org/cgi-bin/mailman/options/linux-elitists>,
    <mailto:linux-elitists-request@zgp.org?subject=unsubscribe>

So a bit of formail and sed action could easily parse out the link.