Messages Stuck in "Queued" State When Sent to Greylisting Domains

On a Microsoft Exchange 2003 Server, messages to certain domains may get stuck in a "Queued" state and never reach the recipients.

The messages may get pushed out after the server's SMTP service is restarted, patches are applied (which restart the SMTP service), or the server itself is rebooted. This can result in messages being sent weeks or months after they were originally sent. This problem can be sporadic, and may only affect certain domains.

One cause of this issue appears to be related to recipients who use "greylisting." As a method to combat SPAM, certain hosts will reject an initial message with a 400-level SMTP status message. This should cause the sender (Exchange, in this case), to retry sending the message after a short period. Many SPAMmers will not bother to retry, so this reduces the SPAM load on the recipient.

Exchange appears to occasionally have issue with certain greylisting recipients. There are many reports of this issue in various tech forums around the web, but the issue appears sporadic enough that it cannot be replicated for Microsoft to effectively troubleshoot. There are some reports that the issue may be related to Symantec Mail Security for Microsoft Exchange.

One reported solution to this issue is to force the GlitchRetrySeconds registry value, found in HKLM\System\CurrentControlSet\Services\SMTPSVC\Queuing (you may need to create the Queuing key) on the Exchange server to a value of 60 or 120 (value is the retry time in seconds). The default value for this option should be 60 seconds if it is not set, however forcing the value seems to correct the issue for some users. In our case, we forced the setting to 180, and the issue was resolved.

For more information, see the following newsgroup posting and Microsoft Technet posting on setting the GlitchRetrySeconds value.

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