I would like to know how I can configure my Exchange 2010 to not accept SMTP when the recipient is illegal mailbox. e.g. helo hostname mail from: legal@address.com rcpt to: nosuchuser@myserver.com 550 No such user instead of helo hostname mail from: legal@address.com rcpt to: nosuchuser@myserver.com 250 and then getting an NDR

You know you're setting yourself up for address harvesting scripts if you do this?

I am aware of this, but it's mandatory for me. Willing to take the risk of getting spammed. Is it even possible? if so, how do I go about and do it?

Do you have Edge Transport servers? That seems to be the only role that can be set up for valid recipient filtering.

Exchange 2010 provides the tarpitting interval to combat with the directory harvest attack Resources: Enable Anti-Spam Functionality on a Hub Transport Server James Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com