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SMTP maximum recipients may be set too low

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at http://go.microsoft.com/fwlink/?linkid=34707.]  

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 msExchSmtpMaxRecipients attribute is less than 250. By default, the msExchSmtpMaxRecipients attribute is configured for 64,000 recipients. If the Exchange Server Analyzer finds that the msExchSmtpMaxRecipients attribute is configured with a value of less than 250, the Exchange Server Analyzer displays a warning.

From a security perspective, it is a best practice to limit the maximum number of recipients for each message. It is recommended that you leave the msExchSmtpMaxRecipients attribute set at its default value of 64000.

Each organization should determine its acceptable maximum number of recipients on the basis of its own business requirements. However, it is recommended that you not set the maximum number of recipients to a value under 250. Messages that are addressed to multiple distribution lists are likely to have more than 250 recipients. If you set a maximum number of recipients to a value under 250, Exchange must process the remaining recipients by using additional copies of the message. These additional copies cause increased network traffic.

To view and configure the maximum number of recipients
  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, such as Default SMTP Virtual Server, and then select Properties.

  4. Select the Messages tab.

  5. To revert to the default setting of 64000, make sure that the Limit number of recipients per message check box is selected and enter a value of 64000. Alternatively, you can configure this field with any value that you want, or clear the check box to allow an unlimited number of recipients.

  6. 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:

 
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