Comment 65 for bug 357864

A comment from the bug that just got duped to this one which I haven't seen
anyone mention on this one yet:

This is enough of an edge case that I think this would be a good candidate for
implementation as an extension if it's possible to implement that way.

And yes, I'm someone who's dying to have this feature (I'm a domain owner who
makes up addresses for communicating with various entities I don't trust not to
share with spammers ;) , so I don't think it's not important. :)