Sender Filtering

Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2006-04-11

The Sender Filter agent is an anti-spam filter that is enabled on computers that have the Microsoft Exchange Server 2007 Edge Transport server role installed. The Sender Filter agent relies on the MAIL FROM: Simple Mail Transfer Protocol (SMTP) header to determine what action, if any, to take on an inbound e-mail message.

When you configure anti-spam filters on an Edge Transport server, the filters act on messages cumulatively to reduce the number of unsolicited messages that enter the enterprise. For more information about how to plan and deploy the anti-spam features, see Anti-Spam and Antivirus Functionality.

The Sender Filter agent acts on messages from specific senders outside the organization. Administrators of Edge Transport servers maintain a list of senders who are blocked from sending messages to the organization. As an administrator, you can block single senders (kim@contoso.com), whole domains (*@.contoso.com), or domains and all subdomains (*@*.contoso.com). You can also configure what action the Sender Filter agent should take when a message that has a blocked sender is found. You can configure the following actions:

You can configure the Sender Filter agent to reject the SMTP request with a "554 5.1.0 Sender Denied" SMTP session error and to close the connection.
You can configure the Sender Filter agent to accept the message and update the message to indicate that the message came from a blocked sender. Because the message came from a blocked sender and it is marked as such, the Content Filter agent will use this information when it calculates the spam confidence level (SCL).

You can use the Exchange Management Console or the Exchange Management Shell to designate blocked senders and to define how the Sender Filter agent should act on messages from blocked senders. For more information about how to configure the Sender Filter agent, see Configuring Sender Filtering.

Important:
The MAIL FROM: SMTP headers can be spoofed. Therefore, you should not rely on the Sender Filter agent only. Use the Sender Filter agent and the Sender ID agent together. The Sender ID agent uses the originating IP address of the sending server to try to verify that the domain in the MAIL FROM: SMTP header matches the domain that is registered. For more information about the Sender ID agent, see Sender ID.

Important:

The MAIL FROM: SMTP headers can be spoofed. Therefore, you should not rely on the Sender Filter agent only. Use the Sender Filter agent and the Sender ID agent together. The Sender ID agent uses the originating IP address of the sending server to try to verify that the domain in the MAIL FROM: SMTP header matches the domain that is registered. For more information about the Sender ID agent, see Sender ID.