See http://www.slipstick.com/contacts/addauto.htm for various ways to save senders or recipients as new contacts automatically, depending on your version and configuration of Outlook.

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Sue Mosher, Outlook MVP
Author of
Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> outlook express can automatically add a sender's e-mail address to the
> address book as soon as you reply to his/her message. (options menu / send
> tab). Is that also possible in outlook?
>
> Thanks.