This is in reference to the SFMC function of Dedupe subscribers. A previous post says "that SFMC de-dupes by Email Address, not Subscriber Key. So if you have the same email address with multiple Subscriber Keys, it'll pick one and skip the others".
How do I manage preferences returned for the de-duped e-mail address? For example, if I receive an "unsubscribe" from the e-mail send for the de-duped e-mail address, I would want to apply the preference to all occurrences of the e-mail address across the multiple subscriber keys in which that e-mail address occurs. SFMC would only apply the preference to the one subscriber key with that e-mail address that was selected in the de-duping process.