I don't know the size of your institution, so this may not work for you, but I am the auditor of a small community bank, and the way we "audit" returned mail is that every piece of returned mail is initially sent to me. I view all of it and then distribute it to branches, etc. accordingly. I don't do any sort of audit report on this process, but I do view all returned mail.
If ignorance is bliss, there ought to be more happy people.