if users are to have only one of the two smtp addresses, configure each user with the appropriate address. otherwise configure each existing user with the second smtp address (if necessary - either manually or via a directory export/import using a .csv file) NOTE: any new user will be assigned the smtp address that was used during the configuration. this will have to be modified for each user that needs the other address after the account is created.

you will also need to add the additional smtp domain as an allowed inbound domain (on the routing tab of the ims).

also, you will need to modify your relaying rules (you are a responsible smtp admin and you do have these configured correctly to prevent relaying, right??? Microsoft does a terrible job of documenting how to properly configure Exchange to prevent it from being used as a relay. There are 4 KB articles which are vague, and one very good Technet article. The URL for the Technet article is http://www.microsoft.com/technet/exchange/relay.asp.

drop me an email if you have other questions. reddjohn@yahoo.com

john