ASP.NET - unable to send mail to other domain mail ids using smtp

Hi,
 Im sending mails using our company smtp address. I got the problem when i am sending mail to other mails (out side of company domain)showing error "the server rejected one or more recipient addresses. the server response was 550 5.7.1 unable to relay".
if the mail id with in the company, then there is no error and mail sending successfully. My web application hosted in iss.

can any once please help me how to over come this problem?????


Thank you,
Siva kumar goru.

This error message means your employer restricted sending emails to all the emails. He allows emails to only few email. To resolve this error you should contact your IT Team