550 unable to relay

Hi All,

I have 2 CASHT server with NLB, when i try to send email to internet i am getting

550.5.7.1 Unable to relay error.

I have annoynmous users checked at receive connector, Send connector is also there with Mcafee Iron mail defined as smart host, but still i am not able to relay internet emails. I can send emails using telnet from ironmail with no issue. But when i try to send email using telnet or outlook its 550 error.

Any ideas?