I would also post a notice saying your account was hacked. Keep the details to a minimum. Your ex was trying to get attention. There's no need to feed the fire with a long rant. In fact, don't even mention who hacked your account.
Of course, you should block your ex from viewing any of your information online. Block him on any social-networking sites.
Be sure to send your close friends and family direct messages. You can explain the situation in a little more detail. Let them know it wasn't you who sent them inappropriate email.
You didn't bring this up, but I know it happens. Your ex might have access to racy photos of you. Sometimes these get posted online after a breakup.