To set up a person or persons to be replied to in a certain format do this
(copied from Outlook Help):
Change the format for all messages sent to a particular Internet recipient
Open the contact card for the person.
In the E-mail box, double-click the contact's e-mail address.
In the Internet Format list, select the format you want to use for messages
to this recipient.
Notes
You can only change the format for all messages sent to a contact with an
SMTP e-mail address.
For information about plain text messages, see messages in plain text.
WOW Maybe I should write a book!

But then I might have to reply with one sentance vague answers too!
