See if the following article helps:
http://office.microsoft.com/assistance/preview.aspx?AssetID=HA011128331033

Signature
Jocelyn Fiorello
MVP - Outlook
*** Messages sent to my e-mail address will NOT be answered -- please reply
only to the newsgroup to preserve the message thread. ***
> When I try to send emails to people in my personal address book, I
> immediately receive a message: "none of you email accounts could send to
> this recipient." Did I enter names in this address book incorrectly and how
> do I correct this?