We use a third party spam filter called Postini. All of our inbound and outbound traffic goes through this company's servers. Our MX record points to them, they filter and send the mail to us. In their setup instructions, it states that I need to lock down my e-mail relay to restrict inbound SMTP traffic to ONLY their server's IP addresses.
I am very familiar on how to set the relay restrictions in Server 2003 with Exchange 2003 but now we are using Server 2008 Standard with Microsoft Exchange 2010 installed.
I can't find anyone who knows how to do that in Exchange 2010 with a Hub Transport.