Mail Problems with Outlook Express

Everytime I try to send mail I receive the messages:
“The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ‘adrian@mediasat.ro’. Subject ‘test’, Account: ‘192.168.1.1’, Server: ‘192.168.1.1’, Protocol: SMTP, Server Response: ‘550 … Relaying denied’, Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79″
altought the connection with the Mail Server is OK (I can send mail)