You can do that as a part of your signature.
Just setup a signature (I have my name, title, company
name and address, then the disclaimer beneath that, for
example).
You can do that from the Tools menu / Options, Mail
Format / Signatures. Check the options there for outgoing
emails, etc.
PS: Make sure you do that from the main Outlook menu, not
from the menu that you see when youn are writing an email.
Paul