You can't do it automatically. You have to right click on the address and
"Add to Contacts."
> How do I automatically save incoming email addresses in Outlook?
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
> How do I automatically save incoming email addresses in Outlook?