Exchange Server 2003 introduces a new feature: the ability to integrate Real-Time Block Lists (RBLs)—aka DNS block lists—into your Exchange environment. Exchange implements this feature by letting you configure connection-filter rules that incorporate RBLs. Typically, you'll use an external list maintained by a third-party RBL provider such as Distributed Server Boycott List (http://www.dsbl.org), Mail Abuse Prevention System (MAPS—http://www.mail-abuse.org), or Domain Name System Real-time Black List—DNSRBL (http://www.dnsrbl.com). However, you can also create your own RBL. Creating a simple DNS block list can be an excellent means for testing RBLs and getting a feel for how best to use them in your organization. Let's look at how block lists work and step through the process of creating a test list that you can use in your Exchange 2003 environment.
Block List Basics
The standard RBL operates as a DNS zone that filters out the IP addresses of known spam originators according to set criteria (e.g., multiple recipients have reported the address as a spam source, the source is a dial-up subnet of an ISP from which all dial-up subnets are blocked). These criteria can differ from one RBL provider to another, so you'll want to test RBLs before implementing them so that you can find lists that use criteria appropriate to your environment. . . .
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