Proper Reverse DNS format

Posted on 2014-08-19
Last Modified: 2014-08-20
What is the proper format for setting up a Reverse DNS record for PTR lookups. This will be used for sending email. Is it mandatory it match the SMTP banner?
Question by:CanOfWorms
    LVL 28

    Expert Comment

    The short answer is:
    If you are in control of the authoritative nameserver, the first step is to create a reverse DNS zone. The hostname for the zone has to be in a very specific format. It starts with a portion of your IP address written backward followed by
    If for example your IP address is, you start by dropping the final octet (last set of numbers) to give you 192.168.0
    Next, you need to reverse that fragment of the IP address giving you: 0.168.192
    Finally, append leaving you with the completed reverse zone domain of:

    There is quite a nice write-up on it here:
    LVL 25

    Accepted Solution

    Chances are, you won't be the one creating this record. Your ISP (not your domain registrar) is typically the one that has to do this, since they're usually the ones who ultimately control the public IP address that the mail server uses.

    Mail servers typically use forward-confirmed reverse DNS. In order for this to work properly, the FQDN in your mail server's PTR record should match its public host (A) record.

    Getting this record created is usually as easy as contacting your ISP and informing them that you need a reverse DNS record for your mail server. They'll need the mail server's FQDN and its public IP address, and that should be it.

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