[ILUG-BOM] Sendmail problem

Hi All I have a registered domain goldenswan.com and using usernames@goldenswan.com email addresses. goldenswan's mail server is kept somewhere in USA. My LAN mail server(i.e sendmail) setup permits me to send messages to any address where from address shows username@goldenswan.com because I set masquerade as goldenswan.com. It permits me to send messages anyone where messages to usernames@goldenswan.com is delivered locally if user exists in /etc/passwd file. It works fine but for any user not existing in /etc/passwd is rejected. I want a message to any user not exists in /etc/passwd should be considered external message and to be sent to goldenswan.com mail server. Help me to solve this problem.