You can do it with an SQL query. You just have to take their email address and then set the user for that email address to Awaiting Confirmation From Edit as a user state so that no more emails are sent out.
I believe the BD Mails add-on does this. At least I'm pretty sure it's doing it on my forum. This is really an invaluable add-on that perhaps should be made into a feature of xenforo. This does three things: it gets the mail handling off of your server and puts it through Mandrill or another mail handler, it puts bounced users in a special user group, and it notifies those bounced users via a notice, after they log on, that their email is no longer valid and should be updated.
My Mandrill rating is 99% with this thing installed, with 0 soft bounces, 0 hard bounces, 0 unsubscribed, and 1 spam complaint since installation six months or so ago. You can't beat that!
The only downside is that those users with bounced email addresses no longer show in the "total members" count in the sidebar (and there were probably 600 or so), but that tradeoff is well worth the convenience of this tool.