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Antigen Reverse DNS Lookup is Enabled

[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: 2008-01-14

The Microsoft Exchange Server Analyzer Tool reads the following registry path to determine whether the Antigen ReverseDNSLookup registry key exists and is set to a value other than 0 on Exchange 2000 Server or Exchange Server 2003 computers that have Sybari Antigen version 8.0 or Microsoft Antigen Version 9.0 installed.

HKEY_LOCAL_MACHINE \Software\Sybari Software\Antigen for Exchange\

A value other than 0 for the ReverseDNSLookup registry key, or the absence of the ReverseDNSLookup registry key, means that the Antigen Perform Reverse DNS Lookup setting is enabled.

If the Exchange Server Analyzer determines that one of the following conditions is true, the Exchange Server Analyzer displays a warning.

  • The Antigen ReverseDNSLookup registry key exists on an Exchange 2000 Server or Exchange Server 2003 that has Sybari Antigen version 8.0 or Microsoft Antigen Version 9.0 installed and is set to a value other than 0.
  • The Antigen ReverseDNSLookup registry key does not exist on an Exchange 2000 Server or Exchange Server 2003 that has Sybari Antigen version 8.0 or Microsoft Antigen Version 9.0 installed. If no ReverseDNSLookup registry key exists, the default setting of Perform Reverse DNS Lookup setting is enabled.

With the Perform Reverse DNS Lookup setting enabled, Antigen tries to validate Domain Names or IP addresses by performing a reverse DNS lookup to compare to entries in the Antigen Allowed Mailhosts or Rejected Mailhosts lists.

This validation process can cause performance issues on the Exchange server and as a best practice, we recommend disabling the Perform Reverse DNS Lookup setting.

To address this warning, disable the Antigen Perform Reverse DNS Lookup setting.

To disable the Antigen Perform Reverse DNS Lookup setting
  1. Click Start, select All Programs, select Microsoft Antigen for Exchange, and then click Antigen Administrator.

noteNote:
The application to configure the Sybari Antigen products is called
Sybari Client.
  1. In the Connect to Server dialog box, in the server list, select the server you want to connect to, and then click OK.
  2. Click Settings, and then click General Options.
  3. Under Scanning, locate the Perform Reverse DNS Lookup list, and then click Disable All.

For more information about possible Exchange Server performance issues caused by the Antigen Perform Reverse DNS Lookup setting, see Microsoft Knowledge Base article 925602, "Mail flow may stop, and many e-mail messages may remain in the mail queue when you run Antigen 8.0 for Exchange" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=925602).

 
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