SMTP Relaying Restrictions in Conjunction with the Microsoft Exchange Connector for POP3 Mailboxes

In Microsoft Exchange Server 5.5 Service Pack 1 (SP1) and later, there are several different configuration options that you can use to prevent the unwanted relaying of Simple Mail Transfer Protocol (SMTP) mail. Exchange does not enable the relaying of SMTP mail by default.

To support Post Office Protocol 3 (POP3) and Internet Message Access Protocol 4rev1 (IMAP4) clients, or the operation of the Exchange 5.5 Connector for POP3 Mailboxes, you need to change this setting in the Exchange Internet Mail Service (IMS) connector properties. However, this may expose Exchange servers, which are connected to the Internet, to the possibility of being used as gateways for unsolicited commercial email (UCE) or spam.

If you configure the SMTP relaying restrictions in IMS, you may inadvertently restrict the Microsoft Exchange Connector for POP3 Mailboxes from forwarding mail, by way of IMS, to Exchange recipients. This article describes how to configure an Exchange installation, in which you have configured the POP3 Connector to reject the relaying of unwanted SMTP, on a computer that is running Small Business Server (SBS) version 4.5.

To configure the POP3 Connector to work with your Exchange server:

1. Open the properties for IMS in Exchange Administrator.
2. On the Routing tab, click the Reroute Incoming SMTP Mail (Required for POP3/IMAP4 Support) option if it is not already enabled.
3. Click Add to add an entry for your POP3 domain. Type the domain name that your organization uses for SMTP email, and then leave the default setting of Should be accepted as "inbound". Click OK to save the setting.
4. Click Routing Restrictions, and then click to select the following check boxes:
   • Hosts and clients that successfully authenticate
   • Hosts and clients with these IP addresses
5. By default, the list under Hosts and clients with these IP addresses is blank. For routing restrictions to work with the POP3 Connector, add an entry for the IP address of your computer by clicking Add. In the Add/Edit host dialog box, type 127.0.0.1 in the IP Address box, and then type 255.255.255.255 in the Mask box. Click OK four times to save the settings, and then quit Exchange Administrator.
6. Stop and restart IMS and the POP3 Connector by using the Services Control Panel program.

For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base: