How to configure connection filtering to use Realtime Block Lists (RBLs) and how to configure recipient filtering in Exchange 2003
You can use the connection filtering and recipient filtering features in Microsoft Exchange Server 2003 to help reduce unwanted mass e-mail or unsolicited commercial e-mail (UCE) in your organization.
Connection filtering is used to configure Exchange Server to contact a Realtime Block List (RBL) provider to determine whether the computer that an e-mail message is sent from appears in a list of "blacklisted" computers. You can also configure exceptions to these connection filters.
Additionally, you can configure recipient filters to prevent e-mail from being delivered to certain members of your organization or to recipients who are not members of your organization.
This article describes how to configure these filters and how to assign them to a particular SMTP virtual server. Additionally, this article contains a sample mail-flow process to describe where each filter is applied during the mail flow conversation.
To read the full MS KB article click here.