Why would I want to use this you might ask?
Well whe happened to have a customer who only had one E-mail address on his Small Buisness Server 2008. And the other E-mail address was not configured on the Server, but he still wanted to mail to this Mail address. Normally this would not work because the server would try and deliver it locally.
Note: This could also be used to do an Email conversion in phases.
To change this whe need to change a setting in the Exchange Management Console. Let’s open it up and have a look.
Go to Organization configuration > Hub Transport > accepted domains > Then double click the Domain you want to change this for. In the image below I removed the Domain info but you get the idea.
In the next screen you change the setting to “External Relay Domain” this makes it so that every mail you send to your own domain gets routed through the SMTP server. This way if you send an email to this domain it won’t try and deliver it locally on the server.