Thanks for the post and the addition, obiuquido144 - this is helpful.
But it's also important to note that, per earlier posts in this thread, it's probably not a good idea just to resend the emails insofar as (at least in my case), the emails actually ended up being delivered after all. The problem currently, as I understand it, is that the delayed deliveries aren't being reported back to Civi, so the accounts stay on hold, meaning that bounced addresses won't receive subsequent mailings until/unless their status is changed.
Effectively, this means that bounce reports are not terribly useful until this behavior is changed.
I think Piotr's suggestion to treat 4xx SMTP codes (transient errors) as successes is right on the money; addresses should only be put on hold in the case of a confirmed failure, which will happen eventually if the address is bad.
Worst case here is that you end up resending to a bad address, which doesn't really hurt anyone, as opposed to having your mailing list gradually get whittled down. (I have one client whose list of 19,000+ eventually was reduced to about 4,000 before we figured this out.)
I should add here that taking addresses off hold doesn't seem to affect the "user opt out," so it doesn't look like you'd be bothering people who have unsubscribed.
Piotr- please correct me if I'm wrong about anything here - thanks everyone for your help in getting this resolved!