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I have a bunch of domains as relay domains at my sendmail config, i noticed that some dirty botnet is using dns spoof to be able to send emails using those relay domains.

How it works:

a domain zzz.xxx.tld resolves back to, when my server tries to resolve zzz.xxx.tld it falls back to spoof!

Is there anyway to fix/avoid/block this? relaying only on specific server ips would be better?


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1 Answer 1

Do you need to have a hosts entry pointing to Perhaps you could point the hosts to your external IP instead and only allow relaying from localhost.

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I'm not sure what are the implications of not relaying on, some emails are sent by crons and other server internals, not sure if those would be delivered or deferred. –  Rodrigo Aug 23 '10 at 21:58
It mainly depends on the SMTP address they're using, if they're using the external IP or a hostname other than localhost, then that change would break them. –  James L Aug 23 '10 at 22:11

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