Filtering Messages in Exchange 2003

Sender Filtering
Sender filters aren't new to Exchange 2003 (in fact, Microsoft first introduced them with Exchange 2000). Sender filters are almost identical to recipient filters except they process only the "Mail From:" SMTP command. In short, Exchange uses sender filters to drop messages received from a specific set of users or domains. Because the steps for configuring sender filters are so similar to the steps for configuring recipient filters, I focus on a few important points.

As I mentioned previously, you configure filters at a global level and apply those filters to specific SMTP Virtual Servers. Figure 3 shows several check boxes on the Message Delivery Properties dialog box's Sender Filtering tab in ESM. These options modify the behavior of a sender filter.

• Archive filtered messages—When you select this check box, Exchange archives turfed messages in the mailroot subdirectory. If you enable this feature, remember to monitor the amount of disk space that these messages are occupying.



• Filter messages with blank sender— When you select this check box, Exchange drops any message entering the system that contains a blank "Mail From:" SMTP command.



• Drop connection if address matches filter—When you select this check box, Exchange sends a message to the filtered address telling the sender the SMTP service is unavailable. This action is meant to discourage senders from sending future messages.



• Accept messages without notifying sender of filtering—When you select this check box, Exchange drops filtered messages after accepting them. This option turfs messages without letting the sender know that the message has been dropped.

After you configure the sender filter, if Exchange receives a message from an address on the sender-filtering list, it drops the message according to these settings and, by default, generates an NDR. The default NDR message is The e-mail address could not be found. Perhaps the recipient moved to a different e-mail organization, or there was a mistake in the address. The intent is to give the sender as little information as possible. However, you can create custom NDRs (Microsoft will include detailed instructions about how to do so with the Exchange 2003 software development kit—SDK). Like recipient filters, Exchange stores sender filters in AD's Configuration NC. AD stores sender-filtered addresses in the msExchTurfListNames attribute of the default message filter object. . . .