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Exchange 5.5 periodically not responsive

By joemoran ·
I've got an issue that is making me pull my hair out, and I'm hoping someone can give me a lead.

I am running an Exchange 5.5 server and a my own DNS SOA, using my ISP's DNS servers as backup. The system has been solid since September when it wasfirst put in.

Recently though, and for no apparent reason, I started receiving reports from people on the outside saying that they were sometimes not able to get e-mail through to my domain, and that they were receving bounce-backs.

The bouncebacks indicate a "host not found" error for my Exchange server's FQDN. This would seem to imply that it's not a connectivity or a resolution issue, but one where the Exchange server, for some reason, is not responding (or not responding fast enough).

It is difficult to know exactly when this problem is occuring or how long it lasts when it does, but the evidence thus far would indicate that it does not appear to happen very often (maybe once a day) and when it occurs, it does not last for more than a second or two. In almost every case, simply re-sending the message a second time gets it through without incident.

This fact, however, makes the issue maddeningly difficult to track down. I have checked my DNS server, my Exchange server, and checked with the ISP who is providing us with our connectivity (a dedicated T1 line), and can find no evidence of a problem anywhere, but yet the issue persists, albeit on an irregular and upredictable basis.

Has anyone out there experience this phenomenon, or something similar? If so, I would love to get some ideas on how to nail this down.

Thanks in advance.

Joe

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Exchange 5.5 periodically not responsive

by Stillatit In reply to Exchange 5.5 periodically ...

Most mail servers try multiple times before giving the user a bounce message.

Double-check anything that might have changed since it was known to work. Prime suspects in DNS are the SOA record, the A record for the server, and the MX record(s). If your ISP is willing to be a mail backup for you, you can have a high-number MX pointing to their server, so that if someone cannot send to you they can try the backup. Their server then periodically looks for your server to hand off your mail.

Have you installed or changed your firewall lately? You may have blocked access to port 25 on your server or to your DNS. If you have a firewall that can log, try logging all attempts to talk to your Exchange server from outside, and see if you can tell what is happening.

It is possible, but not likely, that someone is running a Denial-of-Service attack against you. Your firewall log should tell you at a glance.

As far as your server not responding:

Is there anything running on the box with the Exchange server that could bog the machine down? This might include virus scanning software (like a scheduled scan of the whole disk), a scheduled defrag, some other application, and so on. Check also that you are NOT running a screen saver which sucks up resources (like anything with 3D in the name).

Good luck.

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Exchange 5.5 periodically not responsive

by joemoran In reply to Exchange 5.5 periodically ...

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Exchange 5.5 periodically not responsive

by joemoran In reply to Exchange 5.5 periodically ...

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