Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I do have a problem which nearly freaks me out. Ok, I do have the following constellation:

There is a Webserver, with the public IPs:


I do have 100 different domains, which are seperated by two providers. All of them, except one are pointing to the .140 address. Their MX records are are showing to two different mail servers. One is configured automatically by the provider and for the rest it goes to one domain which is pointing to a internal mail server in my company. That mailserver works perfectly and I can send emails to whereever I want.

Now I do have a script on the webserver. It is a PHP script, and PHP is configured that it uses the localhost with the smtp port set right. mxtoolbox and mailradar have positive results.

When I send mails from this PHP script, lets say to some mail addresses, where they do a reverse DNS PTR check, i get errors like:

Mar 17 21:55:13 *************** postfix/smtp[23695]: **********: host[] refused to talk to me: (mxgmx004) Nemesis ESMTP Service not available 554-No SMTP service 554 invalid DNS PTR resource record

And of course, the mails are not be sent correctly. When I send a mail to a server, which is not checking the reverse DNS I receive the mail with the following header:

Received: (qmail 27829 invoked from network); 19 Mar 2013 13:10:48 +0100
Received: from unknown (HELO ****************) (
  by ******************* with SMTP; 19 Mar 2013 13:10:48 +0100
Received: by ************ (Postfix, from userid 0)
    id ************; Tue, 19 Mar 2013 13:07:49 +0100 (CET)
Subject: This is subject
To: <>
X-Mailer: mail (GNU Mailutils 2.2)
Message-Id: <20130319120749.872613D674B@*****************>
Date: Tue, 19 Mar 2013 13:07:49 +0100 (CET)
From: root@*************** (root)

This is Content

I see, it says, "from unknown" in the received part. The question is now, who or what is responsible for this? Is it the webserver, where I need to change something in the postfix configuration? Is it the provider for the domains, where I have to set any additional addresses or maybe change anything? Or is it the isp, who has to be active here and change...whatever he can change?

I somehow assume, that its Postfix, but I dont know, what to change there. This is my configuration:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
append_dot_mydomain = no
readme_directory = no
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
myhostname = *************
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = *************, localhost.localdomain, localhost
relayhost =
mynetworks = [::ffff:]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
share|improve this question
up vote 2 down vote accepted

You need to set reverse DNS (PTR) records for your IP address(es). Contact the entity that assigned the IP addresses to you.

share|improve this answer
Well, in fact, a while ago I moved the server to some newer one. And the configurations for ip addresses and stuff hasn't changed at all. So in my opinion it just must have to do with the server configuration. Or am I that wrong? – Keenora Fluffball Mar 20 '13 at 8:17

You need to set closed reverse DNS loops for your IP address(es).

IP addres -> (PTR record) -> DNS name -> (A record) -> IP address

Has your ISP set PTR record for

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.