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Sorry if this has been asked before, but I didn't find an answer to this question, I've 2 servers: djondb.com and taskgeo.com, both domains hosted in the same machine, and same ip address, the dns records "A" work well and resolve properly to each server, now the djondb.com uses google as email service and the server taskgeo.com is using postfix/spamassassin/etc to configure a local mail server. (This is due to a limitation on the number of free accounts provided by google), now the question is around the configuration of the reverse dns, in godaddy I've 2 domains, in the djondb.com I put all the mx and ptr records suggested by google and that works well, on the taskgeo.com I created the following TXT/PTR record:

v=spf1 a mx ptr ptr:5.39.93.221 ~all

somehow the service https://www.whatsmydns.net/#PTR/5.39.93.221/email.taskgeo.com to check the reverse dns, keeps jumping from the original name of the machine ns3280134.ip-5-39-93.eu assigned by the host provider and the real name of the server (taskgeo.com), I checked every 5 mins and the servers from New York (to name just 1) changes from email.taskgeo.com to ns3280134.ip-5-39-93.eu, and back to email.taskgeo.com I'm not sure if this is a refresh problem of the dns and it will become stable in a few days or if there's a ptr pointing somewhere that is forcing the dns to change the name assigned to the IP. something like: PTR record in djondb.com is pointing to something wrong and PTR record in xyz.com is pointing to something right, therefore they keep stepping into each other toes.

Maybe you figured this one out, but I'm not an expert on DNS, and mainly I'm trying to figure out this reading a lot of different posts, but I'm completely lost on what I'm doing and I'll appreciate any suggestions to point me in the right direction.

basically what I want to know is, having 2 different domains on the same machine, with the same ip address, is this PTR record "v=spf1 a mx ptr ptr:5.39.93.221 ~all" in the server taskgeo.com right? should they match (djondb.com and taskgeo.com) the same value in both domains configuration?

How do I trace what is wrong with the above configuration?

Thanks in advance.

  • 1) "v=spf1 a mx ptr ptr:X.X.X.X ~all" is a TXT/SPF record, not a PTR record. 2) I'm not sure how you expect us to diagnose a DNS problem where all of the pertinent details have been redacted. We can speculate, but this happens so frequently that it's usually not worth the time of our DNS experts. – Andrew B Mar 29 '16 at 15:14
  • I agree with Andrew. SPF reconds have nothing to do with reverse DNS. First try to understand DNS basics and configure your system. Then, if something goes wrong, elaborate your question. – Ra_ Mar 29 '16 at 15:59
  • Thanks, I updated the question with the details required, I thought it was enough to understand the problem, but I guess I was wrong. Agree with @Ra_ I understand the basics of DNS and how this works, but I'm having problems to understand the reverse DNS (based on what I've read it's the reverse dns lookup the way servers try to avoid spam, so based on some tutorials I read that I need to configure the SPF properly or my server will be listed as spam, so what am I missing here? the blogs I've read say that I need to configure the PTR record to do this. – Cross Mar 29 '16 at 16:34
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With the new information you've provided, I can confirm the following:

  1. The PTR record associated with that IP address returns email.taskgeo.com., which I believe is what you were trying to change it to. I tested both nameservers to make sure that the responses were consistent.
  2. The TTL for this record is 86400 seconds, or 24 hours. It will take up to 24 hours for all recursive DNS servers on the internet to forget the prior value. (if they have learned it previously)

Based on the above, the most likely conclusion is that not enough time had elapsed between the PTR record change and the validation that you were performing. The validation website was making queries against multiple nameservers, and the version of the PTR record cached by each was different.

Once 24 hours have elapsed since your last PTR record change, everything should be consistent. If that is not the case, please update your question and let us know.

Validation method:

# perform a nameserver trace
$ dig +trace -x 5.39.93.221

<snip>

93.39.5.in-addr.arpa.   172800  IN      NS      dns100.ovh.net.
93.39.5.in-addr.arpa.   172800  IN      NS      ns100.ovh.net.
93.39.5.in-addr.arpa.   3600    IN      NSEC    94.39.5.in-addr.arpa. NS RRSIG NSEC
93.39.5.in-addr.arpa.   3600    IN      RRSIG   NSEC 8 5 3600 20160428100200 20160329090200 28284 5.in-addr.arpa. TdKXkprdO6Xkg3RyzRqr+rMhM38ikOPc5FRU0aCZY3REu3Ixm8OzRtLB TuYCYXi/HYwZBm+bN2btlL8xH7/+NWq4CwKxCZ7PEbLeEpsNMYZyqron W91g7lR1Wj4fzDzt6RmM7JJbQd3YtHIxTqU9XiqiY2H+bfHATuduFqNs iow=
;; Received 317 bytes from 202.12.29.59#53(sec1.apnic.net) in 238 ms

221.93.39.5.in-addr.arpa. 86400 IN      PTR     email.taskgeo.com.
;; Received 84 bytes from 213.251.188.144#53(dns100.ovh.net) in 139 ms

# make sure the other nameserver returns the same response
$ dig @ns100.ovh.net +short -x 5.39.93.221
email.taskgeo.com.
  • Wonderful, thanks for your help, I was worried looking at the values changing back and forth, and I thought I did something wrong. – Cross Mar 29 '16 at 16:57

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