Facing issue while creating an alias to a domain

Hi..

I have a windows server 2k8 r2 with exchange server 2k10.

Say I have a domain world.loc.

For eg: I want to create the email addresses for user mailboxes as testUser1@us.com, testUser2@asia.com.

Also I want to join the windows 7 machine with the domain alias (us.com). In this machine I will use outlook to send and receive mails for testUser1@us.com.

I tried it as below.

* creating New Alias us.com for the domain world.loc in DNS manager.

* Active Directory Users and Computers -> Users -> <Right Click Particular User> -> Select Properties -> General -> E-mail. Edited this email address from testUser1@world.loc to testUser1@us.com.

Neither able to join win 7 machine with us.com nor send/receive mails to testUser1@us.com.

Can someone give references or guide on how to achieve these domain/mail aliases ?

Any input is welcomed.

Thanks.