Exchange 2003 emails not sending

Exchange 2003 running on SBS2003 was all going well for last 6 years until last week when users were finding outgoing emails taking around 2 hours to reach recipients. Then this escalated to them getting 'Deleyed delivery' messages and today they are unable to send out any email, with all messages returning after a while with "Delivery to the following recipients has been delayed". The first time a restart of the Exchange services seemed to work, although on attempting to dismount the Store, a c1041733 message was returned "The operation cannot be completed because a backup process of the targeted stores is currently running". Yet no backup was running. A re-start of the services fixed this, which may or may not have been related to the delayed delivery issue. It could just as easily be an unrelated and insignificant issue. But today, several re-starts of the Services and a full server re-boot have failed to resolve the issue, as has a temporary disable of the AVG Security software. The outgoing mail is stacking up in c:\program files\Exchsrvr\Mailroot\VSI 1\queue. I can't see this being a DNS issue as nothing has changed from when it was working ok. Incoming mail through the pop connector is fine. Users can send email ok from all workstations and from the server via pop/smtp mail accounts but not Exchange. In Event Viewer Application Log there are once per hour or so error id 2013 source smtpsvc "SMTP could not connect to any DNS server. Either none are configured or all are down". Looking back, these entries started appearing on 16 August..... but emails were going out 100% ok from then until last week when the delays started.
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Is the server doing the sending or are you using a smart host?

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Nick RhodeIT DirectorCommented:
Check with who is hosting your MX and External DNS and make sure they resolve properly.  You can use MX toolbox to do tests to see if it is outside.  Can also check and see if your blacklisted etc.
Can you actually open the Exchange Management Console? If you can, look at the SMTP connectors - they should have their own reasons for failure at sending emails. What error messages are you getting here? This should be a bit more telling. Can you also export and upload your logs here?

Also, what disk space have you got on your C vol? Exchange 2K3 will crash and burn if there's less than 2GB disk space.
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Simon Butler (Sembee)ConsultantCommented:
Exchange 2003 doesn't care about the free disk space. It will continue to operate until there is 0k.
I will be pointing the finger at AVG. I have had that cause a lot of problems recently. Disabling it isn't enough. You need to remove it and reboot the server to get it to release its hooks.

laurencoullAuthor Commented:
Resolved: It was wrong DNS addresses in the SMTP Virtual Server. But can't figure why it just went wrong today, as these DNS settings have been there for years and not caused any issues. But as soon as I checked with the ISP what the DNS should be and fed in their settings instead, voila!
Maybe check DNS cache settings....
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