>I knew .. this is because there is no user1@lippogeneral.com in server B ..
>my question is: how to set qmail automatically send email to server A if this condition met.. ? ..
>please advise .. thanks a lot in advance

Looks to me like your mail system is not properly set up. There are many ways to solve this problem, but the one I would use is to check your settings so that ALL mail is sent through your SMTP server instead of going first through your local qmail, it is not the most elegant solution, but it will work.

Another way is to check your /var/qmail/control/locals file, tell qmail not to read locals and make sure the MX record is set up properly...