Mail.app has a curious feature, which is interesting if not immediately useful.

If you put a URL in the Subject line of an email, and some text in the body of the message, Webkit (or whatever handles the text in Mail) turns it into hyperlink.

As pointed out in a tip on MacOSXHints , it doesn’t work if you leave the body of the message blank.

The result is a clickable subject in the delivered email:

It’s not clear to me how users could make use of this behaviour, especially since you need to put text in the body of the email to trigger the parsing, text which might as well be the URL itself.

Still, it’s something to blog about ;-)