I want to set up a small mail server. I have got Postfix on Ubuntu working, but now I want to add some level of spam filtering using the zen.spamhaus.org DNS blacklist, and this is not working. The Spamhaus instructions suggest trying this command:
dig +short 2.0.0.127.zen.spamhaus.org
and if I run it on my droplet I get no answer. At home, using my ISP’s DNS server, I do get a reply, so Spamhaus is working fine, it’s the droplet’s resolver that’s not returning anything. The /etc/resolv.conf file includes Google’s public name servers:
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 2001:4860:4860::8844
nameserver 2001:4860:4860::8888
nameserver 8.8.8.8
The Spamhaus instructions mention:
Check what DNS resolvers you are using: If you are using a free “open DNS resolver” service such as the Google Public DNS […] in most cases you will receive a “not listed” (NXDOMAIN) reply […] We recommend using your own DNS servers when doing DNSBL queries to Spamhaus.
Can I configure my droplet to use some DNS server that does return replies from zen.spamhaus.org?
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I’m running into the same problem. Is there any chance that DigitalOcean runs (or will run) internal DNS servers for droplets or will they continue to farm out DNS to Google’s servers?
It turns out it isn’t rate limiting by Google, they just don’t respond properly to the spamhaus queries. I ended up switching my DNS servers to use opendns and the RBL queries are working properly now. They are 208.67.222.222 and 208.67.220.220
Yes, this very much looks like a matter of Google’s resolvers being rate limited
andreas@leto:~$ dig +short @8.8.8.8 2.0.0.127.zen.spamhaus.org
andreas@leto:~$
vs.
andreas@leto:~$ dig +short @127.0.0.53 2.0.0.127.zen.spamhaus.org
127.0.0.2
127.0.0.10
127.0.0.4
andreas@leto:~$
If you want to be querying blacklists, I recommend that you too run your own resolver.
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