SOLVED: How to Add a Global Footer To Hosted Exchange on Office 365

This document explains how to add a non-repeating email footer to your Office 365 Exchange 2010.

Step 10 below will exclude internal emails and step 11/12 will stop the footer from being added over and over again.

1. Sign into mail.office365.com with a user account that has admin rights
2. Click OPTIONS in the top right corner of Outlook Web App (OWA)
3. Click SEE ALL OPTIONS
4. Use the MAIL > OPTIONS menu at the top left to change from MANAGE MYSELF to MY ORGANIZATION. If you don’t see this option, you are not signed in with an Admin account.
5. Click MAIL CONTROL in the menu on the left
6. Click RULES (although you are likely defaulted their already)
7. Click the NEW button
8. Select: If THE SENDER IS IN THE SCOPE OF and set it to INSIDE THE ORAGANIZATION
9. Click the ADD CONDITION button
10. Select THE RECIPIENT IS IN THE SCOPE OF and set it to OUTSIDE THE ORGANIZATION
11. in DO THE FOLLOWING, select APPEND A DISCLAIMER TO THE MESSAGE, type in your footer text and set the fallback action to IGNORE
12. Copy some unique part of the footer text
13. in EXCEPT IF select THE SUBJECT OR BODY MATCHES and paste in the unique part of the footer text (from step 12)
14. name your rule and click the SAVE button at the bottom.

For more detail see THIS Microsoft article