Reverse DNS Record For My IP

Posted on 2008-11-05
Medium Priority
Last Modified: 2012-05-05

I am having a central exchange environment which hosts emails for the root and child domains. All domains have a different email domain name, with only a centralized clustered Exchange server.

All my domains have their own mx records all pointing to the same static public ip address. like mail. domain1.com, mail.domain2.com etc all pointing to a single IP.

How can I create a reverse DNS record in this case as all the emails for different domains flow through the same IP.

Can I have multiple PTR record for the same IP matching all my MX records to that IP?

Question by:Rajith Enchiparambil
  • 2
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LVL 16

Expert Comment

ID: 22885909
Hi Rajith_Enchiparambil,

Best practice is to have only one PTR record per IP address, and for that PTR record to point to a hostname that has an A record pointing back to the same IP address.

So you can have the hostnames pointing to the same IP, but there should just be one PTR record for the IP (any one of those hostnames).

LVL 24

Author Comment

by:Rajith Enchiparambil
ID: 22886129
If I have any one of the hostnames as the PTR record for the IP, won't the reverse check fail when a user with a different email address sends an email through the same IP?

Expert Comment

ID: 22886883
I'm hosting multiple websites on a single server. I have never experienced any problems with having multiple domains reverse look-up records pointing to the same IP address ever.

So in brief:

YES you can.

As to your latest comment, no it won't cause a problem which is why it's a reverse-lookup, It only needs to know the IP address of the domain name it doesn't have to be the only IP address for a domain name.

LVL 24

Author Comment

by:Rajith Enchiparambil
ID: 22886947
Bit confused Sci-Fi-Si.

Is it possible to have multiple PTR records for the same IP?
I have only one IP which has many MX records mapped. So, when I create a PTR record with one MX record name, what happens to the other email domains?
Will they get rejected as they will have an email someone@domain1.com and the PTR record for that IP is pointing to domain2.com?

Accepted Solution

Sci-Fi-Si earned 2000 total points
ID: 22887012
Yes it is, I have about 50 for my single IP - lol

The MX records will have their own domain name, but in the reverst ptr records list they will all be listed under the same IP - this does no harm whatsoever.

>Will they get rejected as they will have an email someone@domain1.com and the PTR record for that IP is pointing to domain2.com?

No as if that were the case and each domain had to have it's own IP address, there would be no way to check which other domain name in the world had the same IP, so this is not a consideration.

Sci-Fi Si

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