Adding email accounts in Exchange

I have a client that would be able to add various email accounts to Exchange.
This brings up several (possibly silly) questions:

* Do you have to setup a new user account in ADUC in order to have an email
account in Exchange? If not, how do you set one up without entering it in
ADUC?
* Is it possible to setup a 'variable' email account to where anything in
front of the @ symbol is valid and gets routed to a specific account? (Please
note that I have advised against setting something like this up due to the
spam factor alone!)
* Is there anyway to map/route multiple email addresses to a single user
account? Could this be done with aliasing?

Thanks for any helpful replies!