Excerpts from my correspondence with the guy at DNSReport.com. All the text is from
him; I've edited out my part.
Commments?
--- begin forwarded text
When our DNS servers receive a request for the A record of dnsreport.com, they will
immediately reply with a "nodata" response. ...
The problem seems to be that SIMS chokes when it gets the "nodata" response (which
indicates that the host name *is* valid, but there is no A record for it), as opposed
to a "nxdomain" response (which indicates that the host name is not valid, and there
is no A record for it). "dnsreport.com" will return the "nodata" response, whereas
"madeuphostname.dnsreport.com" would return a "nxdomain" response (and SIMS won't
choke on that).
I'm guessing that the DNS engine that SIMS uses doesn't process the "nodata" response
correctly, gets stuck in an infinite loop, and times out after 45 seconds.
...
<sigh> We've been over this -- if you are right, it should take the same amount of
time on average to resolve "dnsreport.com" and "www.dnsreport.com" (unless the lookup
is not following the RFCs). And, the response the second time should be immediate, as
the results should be cached. The RFCs (RFC2308) require the DNS server that SIMS
uses to cache the negative response for dnsreport.com for 24 hours.
Try using "HELO somemadeuphost.dnsreport.com" (which gives a "nxdomain" response), and
you'll see a result in about 2 seconds. Try "HELO dnsreport.com" ("nodata" response),
and you'll see it takes 45 seconds.
...
It does delay 45 seconds if the A record doesn't exist, or possibly if the "nodata"
response isn't handled correctly.
... you'll need a mail server that caches the DNS entries, and handles the "nodata"
response according to the RFCs. :)
...
I think at this point the only issues are that SIMS isn't caching DNS entries, and is
choking on the "nodata" response; and that the DNS report isn't following RFCs
completely (although I think the only issue now is the "RCPT TO:" that uses
example.com, which causes a delay -- probably because of the "nodata" response for
example.com).
If I've forgotten something else on our end, please let me know ...
-Scott
--- end forwarded text
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