RDNS errors, ISP or Webhost issue.

Posted on 2007-07-19
Last Modified: 2008-01-09
More and more I see email servers check for RDNS resolution. I'm not very clear on the process of RDNS. I usually configure MX record for the server at the webhost level. It is easier for me to deal with Webhositng companies then dealing with ISP's DNS department. So we usually create an A record and MX record for a mail server. The question is regarding RDNS. If a server is resolvng an RDNS address, who is responsible for RDNS? Is it ISP? because ip addresses belong to ISP? An example would be a domain name
They fail the RDNS test at website. Some of their emails are not being able to go out. Do I need to cntact ISP and ask them to create a RDNS error for the address, which is hte address of their a record of
Question by:mavrukin
    LVL 4

    Expert Comment

    you will need to contact your ISP who is providing you an IP address.  i am assuming you have statice ip.  and if that is case, then your ISP and let them know that you want your IP to have a PTR record pointed to your mail server hostname.

    so if your mail server is "", then you will request your ISP to have the PTR record point to "".  once PTR record is configured by your ISP, it generally takes couple days to replicate.

    what kind of errors are you getting, in particular, any bounce back, rejected mails...etc, etc.

    i hope this helps you.
    LVL 1

    Author Comment

    yes, it does help.
    Is PTR the same as RDNS? some ISPs will require an exact comand line for DNS servers. Do you have an example of PTR (RDNS) script? Also, I'm familiar with nslookup and I know how to check for MX record, and A record for example. Is there any way to see what kind of RDNS entry a specific domain has via comand line?
    LVL 4

    Expert Comment

    PTR is a pointer record in your ISP DNS configuration that they will modify.  they will need to make those changes for you.  ISP should perform this tasks for you unless you have access to their DNS record panel.  just use to check rdns now.  and once the ISP makes the changes, you can come back and check again.
    LVL 39

    Expert Comment

    Yes, a PTR is the same as RDNS.

    If your ISP says they need the exact script for their DNS server, ask to speak to someone who understands what DNS actually is.

    All you need to ask for is a PTR for "yourip" pointing at "yourfullservername"

    LVL 1

    Author Comment

    Still little confused.
    The email server we talked about; comes up with no RDNS setup.
    However when I run the tests against mail.gladiustechnoloige.scom (another one setup by me)
    it looks like the RDNS is setup, however i never told ISP to set it up, and it does not look like its setup correctly. Could you please look at the output and tell me how it should be setup. Then I think I will understand.
    Here is the output for It does not seem right. is not an IP address, so I am using (the A record for
    Location: United States [City: Plano, Texas]

    The  reverse DNS entry for an IP is found by reversing the IP, adding it to "", and looking up the PTR record.
    So, the reverse DNS entry for is found by looking up the PTR record for
    All DNS requests start by asking the root servers, and they let us know what to do next.
    See How Reverse DNS Lookups Work for more information.

    Asking for PTR record:  
  says to go to (zone:
    Asking for PTR record:  
  [] says to go to NS2.SWBELL.NET. (zone:
    Asking NS2.SWBELL.NET. for PTR record:  Timed out [at].  Trying again.
    Asking NS1.SWBELL.NET. for PTR record:  Reports [from]

    Answer: PTR record: [TTL 7200s] [A=]

    To see the reverse DNS traversal, to make sure that all DNS servers are reporting the correct results, you can Click Here.
    LVL 4

    Accepted Solution

    by: looks like your IP has a PTR record pointing to your ISP.  you will need to contact SBC and speak to their tech support and have them setup PTR record pointing back to your exchange server.  unless this is done correctly you will continue to have issue.

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