North American Network Operators Group|
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Re: Criminals, The Network, and You [Was: Something Else]
My mail servers return 5xx on NXDOMAIN. If my little shop can spend not too much money for three-9s reliability in the DNS servers, other shops can as well. When I first deployed the system, the overwhelming majority of the rejects were from otherwise known spam locations (looking at Spamhaus, Spamcop, and a couple of other well-known DNSBLs). The number of false positives were so small that whitelisting was easy and simple to maintain.
If a shop is not multihomed, they can contract with one or more DNS hosts to provide high-availability DNS, particularly for their in-addr.arpa zones.
It's not hard. Nor expensive.
Paul Ferguson wrote:
Re-sending due to Merit's minor outage.