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 protected], and to that, I have an alias, 
[email protected]. 
Whenever I send an email to 
[email protected], I examine the headers, and I see the "To:" 
field being correct, "To: 
[email protected]". All is well. 
I recently set up another user, 
[email protected] to function as a multipurpose mailbox. I aliased "
[email protected]" to the services account in the same method that I did "
[email protected]", however nothing I have sent to "
[email protected]" actually goes TO "
[email protected]". All of the headers say "To: 
[email protected]". 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?