[otrs] More questions about CustomerID/Company

It seems CustomerID and Company don't work the way I would think they would. I expected to be able to assign a customer_user a CustomerID and then the Company that I created with that CustomerID would show up when I receive an email from them. However when I get an email from the email address I used when creating a customer_user it doesn't show the Company or CustomerID I assigned to it. Am I way off base here? Is it possible to do something like what I want? Is there better documentation somewhere on the Customer portion than in the admin guide? Thanks :) Paul