Set up a custom message header for email

To append a unique message header for identification reasons to every message in Exchange. You can achieve this by setting up a Transport Rule.

1: Open Exchange management Console and browse to 
Exchange>Organisation>HubTransport.
  2: Click on Transport Rules and select New Transport Rule in the action pane.
  3: Enter the name of your new transport Rule, click Next.

4: Put a check in the box for "From users that are inside or outside the organisation", select inside or outside from the option below, click next.

5: Select "Set headers with Value"

6: Click on the 2 parameters below and set the header and the value, click Next

7: Click Next.

8: Click New.

9: Send a test and observe the header information in Outlook.