Okay, an update for readers:
I too have had the error as reported in this thread and I have determined it is due to my localised use of the microsoft 'DNS SERVER' on my windows Server 2008 box. (I never got these errors until I implemented that, and also shown that if the dns cache was flushed/cleared the error goes away for some hours before returning again.). To be sure, the reason for the use of a local DNS Server as opposed to standard use via the ISP supplied DNS was the significantly improved scantime for spamassassin and hmailserver from 15 seconds down to 3 or 4).
So, as the error seemed to only apply to the SPAMHAUS.ORG blacklist lookups, I decided to exempt that domain from my local dns cache and had my dns server forward requests for it directly out to my ISP's default DNS: I added a 'conditional forwarder
' in the DNS Server setup:
to IP/FQDN: <my ISP's DNS server address - either in IP form or FQDN form>
Since doing so I have no longer received this error.
OF course, who knows whether there are other DNS query failures going on generally - but I have no evidence anywhere that there is (no failed internet page loads, win log events or anything), anywhere at all; It was only the hmailserver logfile for SPAMHAUS.ORG lookups that had an error with DNS and reports as such. As this is the only thing obvious and of concern I maintain this single 'fix' for the problem.
As a further note, (for readers in the same situation using MS DNS Server) I also note that the 'scantimes' that it takes spamassassin and hmailserver to evaluate a message slowly creeps up later in the day. I noted that by clearing the DNS Server cache, this scantime comes down again (to 4 or 5 seconds instead of 10 or 11). So, I have implemented in my 'nightly' housekeeping routine the following command
this clears the DNS Server cache daily and therefore brings the scantimes down again.
So it is clear that DNS SERVER (as Sniff has also identified) was the cause of some problems/inadequacies. I found for my simple setup that adding the 2 'fixes' above keeps things working as best as can be expected given the choice of software in use.