I've got a hosted exchange solution through Apptix, which isn't the problem, I think, but it may be relevant.
I have my main account, email@example.com, and to that, I have an alias, firstname.lastname@example.org.
Whenever I send an email to email@example.com, I examine the headers, and I see the "To:" field being correct, "To: firstname.lastname@example.org". All is well.
I recently set up another user, email@example.com to function as a multipurpose mailbox. I aliased "firstname.lastname@example.org" to the services account in the same method that I did "email@example.com", however nothing I have sent to "firstname.lastname@example.org" actually goes TO "email@example.com". All of the headers say "To: firstname.lastname@example.org". This makes it extremely difficult to filter based on headers alone.
Does anyone have any feedback on what settings I would need to look at in order to fix that?