How Query-Based Distribution Groups Work
When a message is submitted to a query-based distribution group, Exchange handles the message slightly differently from messages destined for other recipients. A query-based distribution group flows through Exchange to the correct recipients as follows:
E-mail messages are submitted through the Exchange store driver or SMTP to the submission queue.
The categorizer, a transport component that is responsible for address resolution, determines that the recipient is a query-based distribution group.
The categorizer sends the LDAP query request to the global catalog server.
The global catalog server runs the query and returns the set of addresses that match the query.
After receiving the complete set of addresses that match the query, the categorizer generates a recipient list containing all the users. The categorizer must have the complete set of recipients before it can submit the e-mail message to routing. Therefore, if an error occurs during the expansion of the query-based distribution group to its individual recipients, the categorizer must restart the process.
After the categorizer sends the complete, expanded list of recipients to routing, the standard message delivery process continues, and e-mail messages are delivered to the mailboxes of the recipients.
The process differs if a dedicated expansion server is used for query-based distribution groups. In this case, instead of sending a query to the global catalog server for expansion as discussed in Step 3, the e-mail message is first routed to the dedicated expansion server. After the message arrives at the expansion server, the expansion occurs, and the delivery follows the same process as described earlier. The expansion server must be an Exchange 2000 SP3 server or later.