I am presented a mail server setup, that is working well. There's only a small issue, which makes me think, there's something wrong in the DNS setup. It is a small setup with a Debian mail server (postfix/dovecot) behind a router. The router has port forwarding configured and is named "router.intern" (IP So incoming mail gets delivered to the mail server and outgoing mails are also fine. Every time a mail gets delivered, there is a reverse DNS check for the delivering server IP to block spammers. But there's also a reverse DNS check on the router's name:

postfix/smtps/smtpd[8088]: warning: hostname router.intern does not resolve to address

( is a placeholder for its WAN IP.)


domain intern

Why does the mail server try do resolve the router's DNS name over WAN? I'm at loss where to search as everything else is working fine.

  • Sounds like your router is doing either application level proxying or SNAT. You might want to check the configuration settings for its port forwarding. – roaima Jun 10 '15 at 16:47
  • No, checked that. None of both is set. – awado Jun 10 '15 at 17:18
  • Is there any relevance to the address you've written as Is this a literal part of the error or a placeholder you've invented for this question? If it's a placeholder please identify what it corresponds to. – roaima Jun 10 '15 at 17:42
  • Sorry, it's a placeholder. I just edited my post to reflect that. – awado Jun 10 '15 at 17:57
  • Try giving a look here: postfix.org/BASIC_CONFIGURATION_README.html with particolar reference to paragraph "Proxy/NAT external network addresses" – Damiano Verzulli Jun 10 '15 at 19:09

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