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 or if multiple values have been set. By default, the msExchServerBindings attribute is configured for TCP port 25. If the Exchange Server Analyzer finds that this attribute has more than one value set, a non-default configuration message is displayed together with the name of the virtual Simple Mail Transfer Protocol (SMTP) server that has multiple values set.

The msExchServerBindings attribute represents the TCP port on which this 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 includes multiple port bindings, it could disrupt mail flow.

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

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 them to an Exchange SMTP virtual server on another port. In this scenario, an Exchange SMTP virtual server listening on multiple ports may be an acceptable configuration.

To view or modify the SMTP virtual server listening port
  1. Open Exchange System Manager.

  2. Expand Servers, expand an Exchange server, expand Protocols, and then expand SMTP.

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

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

  5. 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.

  6. Click OK to save your changes, and then click OK to exit the Advanced dialog box.

  7. 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: