Outlook has no feature to maintain a "unique return email address that corresponds to that category." You'll need to change the address manually for each message.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
>I have created 4 categories of contacts that correspond to my 4 different email
> addresses. If I right click on a contact to send a new message the return
> email
> address always becomes the default one instead of the unique return email
> address that corresponds to that category.