How to best deal with bouncing email addresses?

[jay5r]

I've got a forum with 27,000+ members. Over the years a fair number of those email addresses have gone bad for one reason or another. I routinely pull email lists and do mailings outside vB. From those mailings I have a list of bad emails (ones that have bounced, etc.) I'd like to take that list and downgrade those users from "Registered Users" to "Awaiting Email Confirmation" but I have no clue how to do that. I also want to make sure that if they've subscribed to any threads via email that those subscriptions are downgraded so emails aren't sent (if that doesn't automatically happen when downgrading their status to "Awaiting...").

Over the years I've tried to keep an eye out here for solutions, but haven't seen any that addressed my particular problem. I find it hard to believe others haven't needed to fix this issue - so just wondering what people do to deal with members' bad email addresses?

Oh yeah, I'm running v4.2.1.