Dear All, How one can restrict exchange 2003 as becoming an Open relay.

Hi Sandesh, These links will explain you in detail about how to restrict SMTP relaying How to block open SMTP relaying and clean up Exchange Server SMTP queues in Windows Small Business Server http://support.microsoft.com/kb/324958 Securing Exchange Communications http://www.microsoft.com/technet/security/prodtech/exchangeserver/secmod44.mspx#EQEAG

I am sure, this webcast would be helpful to you which demonstrate how to block open SMTP relay... http://support.microsoft.com/servicedesks/ShowMeHow/101904_2.asx

I have replied to similar thread before. you can refer to http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=3876197&SiteID=17.