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Countless emails wrongly blocked as spam after Cisco's SpamCop failed to renew domain name at the weekend
SpamCop - Cisco's anti-spam service - failed to renew spamcop.net over the weekend, causing it to lapse and resulting in countless messages being falsely labeled and rejected as spam around the world.
From what we can tell, this is what happened. When the domain name expired, *.spamcop.net resolved to a domain parking service's IP address. The way that SpamCop's DNS-based blocking list works is that if you, for example, want to check that an email sent from a system with the IP address 22.214.171.124 is legit, you run a DNS query on 126.96.36.199.bl.spamcop.net. If SpamCop returns a valid DNS entry for that lookup, then it's an IP address known to have sent out spam in the past and should be treated with suspicion.