Under Organizational Configuration, click on Hub Transport, go to the Transport rules tab, right click on your disclaimer and select Edit. Click Next, Next, and Next.

On the Exceptions page select “except when the message is sent to users that are inside or outside the organization, or partners”. After checking the checkbox, make sure the selection shows as Inside. Then complete the rule wizard. After this change no messages bound for internal recipients will have a disclaimer appended to the message.