When I reply to certain messages I want the recipient to 'see' a different
email address from the one I am truly sending from. Is that possible in
Outlook?
What your recipient sees in the "From:" field is whatever you put in the
"From:" field yourself. You can change that in the account properties, or
set up a new account with the email address you wish your recipient to see.
However, be advised that you can't control the routing headers stamped by
the servers which handle the email between you and your recipient. So, if
your intent is to mask your identity, a savvy user will be able to "unmask"
you.