yes ofcause I do not want to be in the blacklisted . But you know , I would like to make smtp must authenticate , and a people who could authenticate success could sendmail everywhere he want .
I think that is the better way , because as the administrator , you could not tell the client that which domain he could send to and which not .
So , thank you for answering my question , I've been wating this answer for long time
, and , if you have any idea more about it , give me some of your experience.