Viktor Dukhovni:
> On Sun, Mar 24, 2019 at 09:00:24PM +0000, Nick Howitt wrote:
>
> [ Please avoid pasting "non-breaking space" characters into
> your email. It is tedious to have to convert these to ASCII. ]
>
> > The header is below (x headers and DKIM removed):
> >
> > Return-Path: <g...@hz.gov.cn>
> > Received: from hz.cn (unknown [220.191.208.116])
> > by howitts.co.uk (Postfix) with ESMTP id 6614E401361E
> > for <usern...@howitts.co.uk>; Sun, 24 Mar 2019 10:09:30 +0000 (GMT)
>
> The "unknown" means that either:
>
> 1. The IP did not resolve to a PTR (name) record
> 2. The name did not resolve back to the same IP
>
> In case 2. the IP could have had a reverse name.
>
> > Mar 24 10:09:30 server postfix/smtpd[8102]: warning: hostname
> > mail.hz.cn does not resolve to address 220.191.208.116
> > Mar 24 10:09:30 server postfix/smtpd[8102]: connect from
> > unknown[220.191.208.116]
>
> This is case 2.
>
> > Have I misunderstood something or is something else at play?
>
> Inattention to detail, and/or unfamiliarity of the meaning of
> "unknown" in the Received header.
To clarify,
1) The reverse name (PTR) lookup succeeded. The client would be NOT
be rejected by reject_unknown_reverse_client_hostname.
2) The IP address lookup for the name produced the wrong IP address.
The client would be rejected by reject_unknown_client_hostname.
Wietse
