Can't use "To Address" in the assignment rules

Can't use "To Address" in the assignment rules

Can someone help me with the Ticket Assignment Rules?
I m entering a rule that will use the To address and it does not seems to work.
I use "contains" or "is" but they do not do the job.
Are there any limitation I need to know about it?
What exactly is the To Address? not the Address in the "to:" inside the ticket?