I have in the past used email addresses with plus signs and slashes in them, and some sites refused to accept them. In one particularly vexing case, a mailing list I was on was moved to a new mailing list manager, which happily sent me the list mail, but wouldn't let me unsubscribe because it refused to believe my email address was correct. After repeated failed attempts at contacting the list manager, then postmaster at the offending site, I started bouncing every message from the list with a nasty message.

Try posting a question without checking the notify box. Once the question is posted, you should be able to activate notifications (scroll to the bottom of the page and check the box).