If you would like to create an HTML email footer for all emails you can use Transport rules.
Logon to Exchange management, go to Mail Flow and rules.
Create a New rule.
Give it a name, Apply this rule if……The sender is located Inside the organisation.
*Do the following….. Append the disclaimer; at this point paste in your HTML code.
If you do not see expect at the bottom click more options, add expection, “The subject includes..” and enter RE: FW: as two entries, this prevents the disclaimer been added multiple times.
Save and test.