Updated on 11/15/07 by Wrobinson: You need to add the additional UPN suffix in AD for the users (see <a href=”http://support.microsoft.com/kb/243629″>Add UPN Suffixes to a Forest</a>.
In addition to “UPN Suffixes” you need to go to exchange management and choose the desired user then go to account tab and specify the domain you want to enable as login. You can even change the login name, for example if you have email@example.com you can change it to firstname.lastname@example.org
What are you trying to do? Users can use their FQDN in their username login if they want email@example.com.
My Answer: My Actual domain name is @mail.local, Users can login to owa with firstname.lastname@example.org.. But what i am expecting is. I updated my Primary SMTP address as my external domain name i.e email@example.com. all users are able to loing with Internla FQDN (i.e firstname.lastname@example.org), what i am expecting is to loing user with Primary SMTP address which i canged in Reciepent policy to take effect (i.e email@example.com) Let me know if you still have any doutbs