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I get this error when checking my DNS with an external tool:

Spam recognition software and RFC821 4.3 (also RFC2821 4.3.1) state that the hostname given in the SMTP greeting MUST have an A record pointing back to the same server

It essentially states this path:

mail.xxxx.com. -> mail.xxxx.com -> (IP of main server) -> xxxx.com

Now my postfix greeting appears as so:

$myhostname ESMTP $mail_name

Is the problem because $myhostname is mail.xxxx.com and that is re-pointing to mail.xxx.com and THEN to my main server? I think I should change it to $mydomain

I would like to get some insight before I edit yet another DNS entry incorrectly.. Thanks

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2 Answers 2

up vote 2 down vote accepted

The error message seems clear to me:

The DNS serving your zone must contain an A record (or AAAA if IPv6 but not a CNAME) equal to the hostname contained in the greeting message sent by your SMTP server. That's a requirement of RFC 2821.

In your case, if the hostname announced by your smtp server is "mail.exemple.com", then anybody must be able to resolve mail.exemple.com.

You can check your DNS records using dig. The result should be the following:

dig mail.exemple.com A +noall +answer       
;; global options:  printcmd
mail.exemple.com. 3600   IN      A       192.0.2.5

Your DNS zone and SMTP configuration must be set in adequation.

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+1 It's also worth mentioning that it may take some time until your test tool updates their cached DNS records, if you have just added a new A record. –  Groo Jun 7 '11 at 6:48

Well I answered my own question there, $mydomain (i.e. xxxx.com) should be used instead of $myhostname (mail.xxxx.com). I had seen this asked a lot but could not find any answered in search engines, so I guess I will leave this here. :)

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