Exchange 2007 have a default behavior : when you create a new distribution group and try to send an email from an external address, the email is not receiving by this group. Internal email are working :
To change this setting go to :
- Exchange Management Console
- Select the distribution Group, Right-Clic, Properties
- Select Mail Flow Settings Tab
- Select Message Delivery Restrictions and Properties
- Remove the check box : Require that all senders are authenticated.
Clic Ok, and test!