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I had my web hosting provider remove a block of IP's from the Spamhaus PBL on Monday since one of the IP's in the range is our web server and it has forms on the site that are used send mail from the server. The IP shows as not being listed on Spamhaus site after removing it but NSLOOKUPs are still returning an A record for queires against ZEN and PBL. I've tried testing lookups from web based sites such as  http://network-tools.com/nslook/ and I've tested from work and home to be sure it's not an isolated DNS problem. It's been 4 days now since that A record should have been deleted. Why are DNS servers still holding on to that record?

DNS servers all have different timeframes of when they check for new records. We have seen clients that have DNS providers that only update once every 72 hours. In the world of the Internet, this is a LONG timeframe, but it happens.

If you are having a problem sending outbound and/or receiving inbound traffic, think about looking into one of our Email Continuity Solutions (includes use of our trusted Smarthost).

Thanks,
Wendy

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Wendy
MXToolBox Support
support@mxtoolbox.com

It's been a week now and the records are still there. The Spamhaus site says DNS should update in 1 to 2 hours on their FAQ. I think the problem may actually be with the DNS servers at Spamhaus. I say this because I have tried NSLOOKUPs on IP's that are listed on their PBL and no record can be found in the lookup.

I just figured out the problem. I just found out that when doing an NSLOOKUP against a DNSBL you must reverse the octets of the IP address you are querying. It just so turns out that the reverse of my IP address actually is listed in the PBL which is what lead me to believe mine was stuck in DNS because I was querying the reverse of someone elses IP!

 Oops.. :-)

Thank you for posting that. I'm sure that people very commonly do not reverse the octets and so get incorrect results.

Peter
MXToolBox