Outlook won't recogize the address when I try to reply

[unterseeboot]

When I reply to a message Outlook puts the person's name in the "To:" field
but it does not resolve that name with the person's email address so I get a
message that says "Microsoft Office Outlook does not recognize Joe Blow" and
also "No suggestions". If I cut and paste a real address like
"(e-mail address removed)" into the "To:" field then the message will be sent, but
this is a real pain to have to do for every reply. It MUST be an easy fix
but I can't find it!

Thanks!