This email message cannot be delivered because the email address is no longer valid:

Issue: User tries to send email to her email alias, but got this error "This email message cannot be delivered because the email address is no longer valid: User was still able to send the email Resolution: The email alias in the nickname cache file is corrupt. Remove the alias and problem is resolved Follow the steps in the article link below to reset nickname and automatic completion caches in Outlook http://support.microsoft.com/kb/287623