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I'm trying to find why postfix rejected the incoming mail the line from mail.log is:

NOQUEUE: reject: RCPT from unknown[]: 450 4.7.1 Client host rejected: cannot find your hostname, []; from=<some@email.address> to=<another@email.address> proto=ESMTP helo=<yyy.yyy.yyy.yyy>

host yyy.yyy.yyy.yyy returns:

yyy.yyy.yyy.yyy has address

Does postfix reject incoming email because of different IPs ( vs ?

Many thanks

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up vote 2 down vote accepted

I'm thinking the RCPT from unknown could be a factor - the mail session should go something like this:

Out: 220 ESMTP Postfix
Out: 250
In:  MAIL From: <>
Out: 250 Ok
In:  RCPT To:<>

Postfix at this point will perform a DNS lookup on and if the lookup matches the ip of the server connected it will proceed, otherwise after you enter RCPT TO..... you will get:

Out: 450 Client host rejected: cannot find your hostname, [x.x.x.x]

The real way to fix this is by ensuring you can look up the mailservers in the DNS (should have PTR records as well as A records).

A crude fix is to edit your postfix config so this check is not enforced.

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This problem could be caused by several factors, please check the following:

1) On the Postfix configuration file, ensure that the mail url is properly setup as it is on your DNS file configuration, it should follow something like :

2) Enable Open Relay with Authenticated users (users that can send/receive should be on an specific group), that way, you will be able to, send emails from any location with your user or any user registered on your system. Be carefull while configuring open Relay, because it can be used to send fake mail.

3) Ensure the ip address is not blocked in Iptables.

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Hi Gerson, the problem is not that postfix doesn't work at all. I', just investigating why emails from that particular address are being rejected. My company domain & emails work so this question is not related to postfix configuration on my server. – Kuba Zygmunt Feb 20 '12 at 21:17

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