Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries the Active Directory® directory service to determine if the value for the msExchSmtpMaxMessageSize attribute has been altered from the default value of 0. By default, the msExchSmtpMaxMessageSize attribute is configured for unlimited message size. If the Exchange Server Analyzer finds that this attribute does not have a value of 0, and Exchange is not running on Microsoft Windows® Small Business Server 2003, a warning message is displayed.

The msExchSmtpMaxMessageSize attribute represents the maximum size of each SMTP message that can be sent or received. From a security perspective, limiting the maximum size of SMTP messages that can be sent to and received from the Internet is a best practice. However, for internal SMTP messages, such as those that travel between Exchange servers in the same organization, it is recommended that you leave the msExchSmtpMaxMessageSize attribute set to 0.

Internally, Exchange uses SMTP messages to handle tasks such as public folder replication. If the msExchSmtpMaxMessageSize attribute is configured with too low a limit, it could cause public folder replication problems and other intra-organizational message delivery failures.

If this Exchange server is a bridgehead server that transfers SMTP messages to and from the Internet, you may be able to safely ignore this warning. If this Exchange server handles internal SMTP messages, you should change the value for the msExchSmtpMaxMessageSize attribute back to its default setting of 0.

If you set the message size limit too low, it could prevent offline address book replication between Exchange Server computers. For more information about this issue, see the Microsoft Knowledge Base article 326154, "XADM: The OAB Does Not Replicate If You Set a Message Size Restriction at the Transport Level," (

To view and configure the maximum SMTP message size

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

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

  3. Select the Messages tab.

  4. To revert back to the default setting of 0, clear the Limit message size to (KB) check box. Alternatively, leave this box checked and configure any value that you want.

  5. Click OK to save the changes and to close the Properties dialog box of the SMTP virtual server.

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