From: Sandy Drobic (postfix-usersjapantest.homelinux.com)
Date: Thu Nov 02 2006 - 02:28:18 CST

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Eugene Geldenhuys wrote:
> Hi
>
> I am new to the list and have tried to find the answer to my question
> in the archives and
> elsewhere on the web.
>
> I am interested in the mechanism postfix uses to resolve names, the
> reason I ask is because
> after implementing
>
> smtpd_client_restrictions = reject_unknown_client
>
> in main.cf, I am seeing messages like this in the log:
>
> scylla postfix/smtpd[11408]: NOQUEUE: reject: RCPT from
> unknown[203.161.126.147]: 450
> Client host rejected: cannot find your hostname, [203.161.126.147];
> from=<someonesomewhere> to=<someonemydomain> proto=ESMTP
> helo=<tara2.wa.amnet.net.au>
>
> I left the hostname and address intact, if you resolve the address,
> you get:
>
> Non-authoritative answer:
> 147.126.161.203.in-addr.arpa name = tara2.wa.amnet.net.au.
>
> which exactly matches the hostname.

Unfortunately, not dns a record exists for tara2.wa.amnet.net.au.
reject_unknown_hostname will reject all clients that do not have a
matching forward and reverse dns record. See details here:
http://www.postfix.org/postconf.5.html#reject_unknown_client_hostname

Be careful with all checks that have "unknown" in their name. They are
likely to reject desired mails.

Sandy
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