How to send as/from a distribution group with Exchange 2010

To grant a user the permission to send from a distribution group you will need to open Active Directory with the view set to “Advanced” then open the properties of the Distribution group you wish to modify, and select the “Security” tab. Click the “Add…” tab to add the users who will be sending as the group.
Once you’ve added the users, check mark Allow for “Send as” under “Permissions for SELF” make sure to uncheck all other permissions.
Remember to allow time for the changes to replicate, and send a test message to you to confirm the changes took effect.