I always thought that the return-path header was used for bounced messages, so I have my email newsletter software setup to unsubscribe anyone whose email address replies back to the return-path email address.
But recently some users started telling me their out-of-office replies where unsubscribing them. Do out-of-office replies get sent to the return-path on some email servers?
I could check all emails to that address and see if they have the "message/delivery-status" content-type in one of the parts, but I wasn't sure if this was necessary.