IIS SMTP LDAP routing, WTF

Windows 2003 Server has a SMTP server, hosted in IIS6. This SMTP server has a feature, LDAP routing.

The documentation for this feature is pretty minimal:

With the LDAP Routing tab, you can configure the SMTP service so that it will consult an LDAP server to resolve senders and recipients. For example, you can use Active Directory directory service as an LDAP server, and use Active Directory Users and Computers to create a group mailing list that is automatically expanded on the Simple Mail Transfer Protocol (SMTP) virtual server.

Resolve sender and recipients?? How, when, based on what attribute? And what if not resolved? And what if the user is resolved? Can it be used for SMTP authorization?

Well one thing it can do is provide AD integration, so mailing groups can be created. See this tread http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/2003_Server/Q_21938977.html with the interesting title "How does LDAP Routing (for the SMTP service) work? In particular together with AD"

I someone knows some decent documentation, please let me know!