The worst one is when they successfully deliver their bounce to the Return-Path but then corrupt the To on the bounce to be the To on the original message and then copy their Message-ID into the original message, thus removing any chance of successfully processing anything. I never figured out the actual MTA that was doing this, but Lotus Domino was involved.
shakes fist
You may get your whole email back, or just the start. The message may tell you what went wrong, it may not. It may tell you what email address you tried to send to that failed, that may be missing (some mail servers actually redact it).