A number of administrators have reported an SMTP greylisting problem on Exchange Server 2003 Service Pack 2 (SP2). Email sent from an Exchange 2003 SP2 machine to another mail server using greylisting does not get delivered. But it doesn't fail either -- it just sits around in a kind of digital limbo until the SMTP service is stopped and restarted.
"Greylisting" is a relatively new spam-fighting technique that filters out spam by causing the first delivery attempt from any given mail server to fail. Since most spam servers are too busy trying to crank through a delivery queue of hundreds of thousands of email messages, they don't tend to retry. A legit mail server will retry after a certain interval.
The SMTP greylisting problem on Exchange Server 2003 SP2 is extremely bad news if you're delivering email regularly to other servers that implement greylisting, since it could mean a lot of email stacking up in your SMTP queues and not getting sent.
So far, there appear to be three workarounds:
- Stop and restart the SMTP service on a schedule.
This is extremely easy to implement -- just create a batch file with the two lines:
net stop smtpsvc
net start smtpsvc
Run this once a day using Scheduled Tasks, preferably during off-peak hours. (The downtime incurred by doing this will probably not be too large, but it's still best to set it to happen during a time when not much will be affected.)
- Use a smart host to deliver email.
This isn't always feasible, unfortunately, but it does seem to help avoid this problem when implemented.
- Set the Glitch Retry key in the registry.
If a delivery fails in the Exchange Server SMTP queue for any reason, it's placed into what's called a "glitch retry state" for 60 seconds. This is done so that if whatever is preventing email delivery is only transient -- for instance, a network patch cable fell out of its socket for a second, but was quickly plugged back in -- the mail in question won't get sidelined for too long.
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People have theorized that the glitch retry interval mechanism may not work under certain conditions unless the timeouts are explicitly set in the registry.
To do this, create the DWORD value GlitchRetrySeconds in HKLM\System\CurrentControlSet\
Services\SMTPSVC\Queuing (you may need to create this key as well) and set it to 60. Then, stop and restart the SMTP service. Some folks have reported getting good results with values up to 120 seconds as well.
Note that the GlitchRetrySeconds value is usually set lower, to prevent massive amounts of email messages from queuing up. If conditions gets worse across the board when you put this fix into place (you may want to give it a few days to see how it plays out), chances are something else may be causing a bottleneck.
About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.
MEMBER FEEDBACK TO THIS ANTISPAM TIP
Thank you for the article on greylisting. We have been having some issues within the past several weeks that this article seems to explain perfectly.
Keep up the good work…
—David J.
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What about the hotfix from Microsoft? It also looks like a call to PSS could solve the issue. The following Microsoft KB article has more information, too:
On a Windows Server 2003-based SMTP gateway server, some messages may remain in the queue folder until the SMTP service is restarted.
We use XWall with Exchange 2003 for all of our SMTP email, so we do not have this problem. I guess that could be considered a workaround as well.
—Mike S.
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I have the same issue. Restarting the SMTP service resends the 'queued' messages again and again. It is not a valid option, since too many messages get resent.
—Ron B.
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