On reflection: Return to sender. Not an option?
I think this is different for external and (genuine) internal e-mail. (I've had spam "from" my own address, presumably used because assumed to be whitelisted.)
External e-mail is likely to benefit the business, even if it's just social. it should be delivered as the sender intended.
Having reflected on the unwanted harassment question, internal e-mail should return to sender, with a covering message that looks like an automated response, but with a hint of doubt. If they want to correct it and send it again, that's up to them. If they're ashamed to, that may be for the best.
I quite often get e-mail intended for a colleague with the same forename, but it is almost never as much fun as the case described.