I am looking for a way to associate multiple email addresses with a single SharePoint user profile which was sync'd from AD (via AD Import). The purpose of this is so that incoming email from any of the addresses could be accepted by a SharePoint library that allows permission to that one user, and all of the incoming items would be identified as being from that user.
I do not want to just allow any address to send to the library, but I also don't want to have to create 10 different AD users to represent 10 different email addresses that may be sending to the library, especially if they all come from the same entity (and for organizational purposes it would be nice to have all those items showing as being from the same user anyway). We have one account in AD to represent this entity so I'd like to be able to associate multiple email addresses with it.
Does anyone know if this is possible? And/or does anyone know the internals on how SharePoint identifies an incoming email to associate it with a user profile? I'm assuming/have observed from testing that it checks the sender address against one or more profile fields - so far I've seen it associate an item to the user when sent from an email that matches the user's UPN, as well as when sent from the email populated in their Work Email field (obviously), but I don't know if there is some other logic going on there as well behind the scenes. Perhaps there is some other multi-valued property that would store all the user's proxyAddresses and be able to identify them that way?
Things I have tried so far include creating a custom multi-valued property to store multiple email addresses. I tried marking it as an "alias" field in the field properties (don't know if that matters here but from the description it seemed like it might), but still, an email address stored in that field was not successfully resolved to my user account. I've also tried just having the user sync with no changes (but with multiple addresses in AD proxyAddresses attribute) but again, only the primary (the one that populates the Work Email field) would be associated with the account - mail sent from one of the secondary addresses was rejected by the library.
This is for SharePoint Server 2016.
Any insight here would be extremely helpful.
EDIT: To clarify, I'm not using the Directory Management Service. This is just a basic incoming email setup (using "advanced mode", w/ the SMTP drop folder on a network share) without the Directory Management features.