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From: JF Mezei on 24 May 2010 14:35
I seem to be having a sporadic problem with spamhaus RBL.

Every so often, I get a message such as:
----
May 24 14:03:32 velo postfix/smtpd[25372]: warning:
183.178.63.69.zen.spamhaus.org: RBL lookup error: Host or domain name
not found. Name service error for name=183.178.63.69.zen.spamhaus.org
type=A: Host not found, try again
-----

nslookup of 183.178.63.69.zen.spamhaus.org works fine.


And when I get that, the spam gets through. But vast majority of times,
the rbl check works fine.



I also added reject_rbl_client entries right after the one for zen, to
include sbl, xbl and pbl. Figured that if the first one failed, perhaps
one of the other ones would succeed and might help pinpoint the problem.

Looking at my logs, this revealed that the error message is repeated for
all 4 lookups (zen, sbl, xbl, pbl). So this would tend to elikminate
random packet loss.


The DNS server is bind 9 on the same machine as postfix. It is not in
"forwarding" mode. It is authoritative for my own local zones (intranet)
and serves as a real DNS server for the rest of my queries. In other
words, it does not depend on my ISP's DNS server.


Apart from using wireshark to collect all DNS traffic from the server
until I spot one such error in the smtp log, what other debiugging
techniques would you recommend ?

In the past, I was using a VMS SMTP server (much more primitive) and
experienced less spam because it didn't seem to have such errors.

And I have yet to see any errors for the njabl rbl which I also check
for. (but njabl catches far fewer spams)

Any hints or suggestions on how to debug this ?





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