Path: ...!news.misty.com!.POSTED.veps.esmtp.org!not-for-mail
From: Claus =?iso-8859-1?Q?A=DFmann?= <INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail(-no-copies-please)@esmtp.org>
Newsgroups: news.software.nntp
Subject: Re: reverse lookup validation failed - how do I fix this?
Date: Mon, 31 Mar 2025 04:58:28 -0400 (EDT)
Organization: MGT Consulting
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Nigel Reed  wrote:

> Mar 31 02:01:39 newsfeed nnrpd[3339866]: ? reverse lookup for
> 2001:41d0:a:280::1 failed: reverse lookup validation failed -- using IP
> address for access

> Interestingly, news.nntp4.net does not resolve back to that IP, it uses
> 2001:41d0:700:1273::

That's probably why the "reverse lookup validation failed"
otherwise someone could map their IP to any name they like
to get around hostname based access control.

MTAs have done that kind of check "for ages".

BTW: does the DNS resolver used by nnrpd give the expected
result for your own IP?