What should I put in my PTR record in my ISP?

[jeremy mendoza]

Guys,

"Pointer (PTR) record www.mydomain.com does not match any fully qualified domain name of the SMTP instances on server (myserver)"

Is my PTR record is wrong?!? what should I put to my PTR can anybody give me any idea/s?

Thanks in adv.

JM

[Rune J. Winje]

Briefly http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS

So to be an official mail server on the internet requires minimum that there is a DNS record called MX record (Mail eXchange) and also an A record (host record).

These forward DNS records should be found at your ISP's DNS server and can be verified by doing nslookup (funnyli enough there is actually a domain called mydomain.com :)

>nslookup
>set type=mx
>mydomain.com

Non-authoritative answer:
mydomain.com MX preference = 0, mail exchanger = mx.mailix.net
mydomain.com MX preference = 5, mail exchanger = amx.mailix.net

So we get two mailservers for mydomain.com which is fine. Select one of them to get their IP address:

> set type=a
> mx.mailix.net
Non-authoritative answer:
Name: mx.mailix.net
Address: 216.148.221.135


So now let's get the reverse DNS lookup for this server:


> set type=ptr
> 135.221.148.216.in-addr.arpa
Non-authoritative answer:
135.221.148.216.in-addr.arpa canonical name = 135.128/27.221.148.216.in-addr.
arpa
135.128/27.221.148.216.in-addr.arpa name = mx.mailix.net
...

So, this response shows that the 216.148.221.135 server is indeed the IP address that belongs to mx.mailix.net mailserver.

Conclusion: If your PTR record does not exist or match the forward DNS then your mailserver will fail verification when trying to send mails to other mailservers that have enabled reverse DNS lookup verification.

Spammers usually send from bogus or dynamic IP's that will fail such tests, since the receiving mailserver looks at the sending IP and finds the domain name via reverse DNS lookup. It then looks to see if this matches the sender information in the mail.

Clearly if some sending IP-address belongs to
dynamic.ip.isp.com
but the mail claims to be sent from
user.name@mailserver.bigcorp.com
it is most probably spam...

Cheers,
Rune

[Susan E. Russel]

This is the best explanation of how to set up PTR records. It verifies that I did it correctly, so thank you.