Hello Tony,
Can you have the user do an Advanced Search for that email address ( the bad one ) and see if it is showing up anywhere.
The Advanced search is the magnifying glass in the top right corner
If you find any matches and get rid of them ( and do the "X" on the address again ) do you still have the issue.
Thank you
Tony
Tony Scholz
System/Network Administrator
SmarterTools Inc.
www.smartertools.com