Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries the Active Directory® directory service to determine whether the configured value for the msExchServerBindings attribute has been changed from the default value of 25. By default, the msExchServerBindings attribute is configured for TCP port 25. If the Exchange Server Analyzer finds that this attribute does not have a value of 25, a non-default configuration message is displayed.

The msExchServerBindings attribute represents the TCP port on which this Simple Mail Transfer Protocol (SMTP) server listens for inbound connections. SMTP virtual servers can be configured to listen on one or more TCP ports. By default, all SMTP virtual servers are configured to listen on TCP port 25, the default SMTP port. If the SMTP listening port has been modified from the default and no longer includes TCP port 25 in its list of listening ports, it could disrupt mail flow.

It is acceptable to change the SMTP listening port, provided that the rest of your internal messaging infrastructure is also modified accordingly. However, generally, alternate ports cannot be used for SMTP virtual servers that accept messages directly from the Internet, as SMTP servers on the Internet send messages through port 25.

Note that the Exchange Server Analyzer is looking at the value for the Exchange SMTP protocol virtual server. This SMTP protocol virtual server may or may not be the SMTP server that receives messages directly from the Internet. There are some antivirus and anti-spam products that are designed to receive SMTP messages from the Internet on port 25 and redirect to an Exchange SMTP virtual server on another port. In this scenario, an Exchange SMTP virtual server listening on something other than port 25 is an acceptable configuration.

To view or modify the SMTP virtual server listening port

  1. In Exchange System Manager, expand Servers, expand an Exchange server, expand Protocols, and then expand SMTP.

  2. Right-click an SMTP virtual server (for example, Default SMTP Virtual Server) and then click Properties.

  3. Select the General tab, and then click Advanced.

  4. A list of IP addresses and ports will be displayed.

    • To change the existing port, select the IP address, and then click Edit. Change the TCP port field to 25.

    • To add port 25 as an additional listening port, click Add, and add the new IP address/port combination. If you are using Connection, Sender or Recipient Filtering, make sure that you select the appropriate check boxes.

  5. Click OK to save your changes, and then click OK to exit the Advanced dialog box. Click OK to close the Properties dialog box for the SMTP virtual server.

For more information about SMTP virtual server settings, see the following Microsoft Knowledge Base articles: