After installing SP2 for windows XP users are not able to use the option: Exhaustively check all address books. Pressing the F9 button doesn’t append the @Domain behind the users address. Trying to send the message anyway the following message is prompt:
Invalid server or network name syntax
When the option “Recipient name lookup”: is set to “Stop after first match” the message can be send without any problems. In this situation the @Domain is appended.