I'm sure that this is not the intended behavior.  I have several users with multiple associations.  If I look in Manage Outbound Queue, if any mail is there, it is always displayed as being for the 1st email address in the person's association list, even though that is not the case.

Anthony,

When you associate multiple addresses with a single user, all of those addresses should go into the same Inbox. Therefore, the recipient's address does not matter, provided you have not associated emails that go into multiple inboxes on the downstream server.

May I know why this is creating a problem on your end?

Please reach out via email if this is causing any problems.

It's only a problem when you don't know who the association is for.  It just seems odd that mail in an outbound queue for user x@abc.com would show up as being for an alias.  It seems it must have been extra effort to code this!