Below is a bounce message that Google sent itself! The context: the original mail was a notification from Google Plus sent to a Gmail account, which triggered a vacation message back to Google Plus, from Gmail, which Google Plus then bounced.

There are so many things that could have been done better here. Google Plus could insert headers of it’s own choice that Gmail can recognise. Similarly the Gmail vacation/out-of-office response could have included headers. Any number of things. Instead we have a bounce, the contents of which a non-technical Gmail user would have little chance of understanding or acting upon.