How to setup reverse DNS for 2 email servers

domain-name-systemreverse-dns

I have an interesting DNS question (well interesting to me atleast).

I just installed an hmail server in our remote office to act as an MX backup in the event our exchange server goes down.

The 2 host names are

mail.campbellsurvey.com
mail2.campbellsurvey.com

mail points to the address 98.XXX.91.XXX
mail2 points to the address 70.XXX.190.XXX

How would I setup a PTR record on the ISP end to reflect both hostnames?

UPDATE

I actually found out from my ISP that I cannot have a backup MX in the office where I wanted it. The reason is our connection in the office has a dynamic IP and they won't assign a PTR to the address.
So this question was useful informational wise, but is a bust in the physical sense. Thanks anyway everyone.

Does the PTR have to point to EXACTLY mail.campbellsurvey.com or can it point to just campbellsurvey.com?

because right now anything passing through the primary static address in our pool (the one used for standard internet) is identified as mail.campbellsurvey.com. My only idea to fix this was to move the mail server to the next available address and give it only it the name mail.campbellsurvey.com but I wanted to see if there was another way.

Thanks in advance.

Best Answer

Set up the pointer for each server to indicate the name of the server on that address. This should be the same as your mail server is using in its banner messages and when issuing HELO commands. PTR records are not significant for incoming messages as the remote server will trust your DNS MX records.

You will want to configure two MX records one for each server with different priorities. The MX records must point to A records. If your SPF records specify MX in the list of permitted senders, you should have no problems with your server addresses.

The PTR records you need are:

98.103.91.146     mail.campbellsurvey.com 
70.XXX.190.XXX    mail2.campbellsurvey.com

Get the appropriate ISP to setup the PTR record for the address they host. You appear to be missing an A record for your mail2 server. There may also some issues with verifying addresses on the second server.

EDIT: So if I was mailing from example.com but my sender's PTR resolved to mta532.mail.google.com or some.other.thing12.smtp.rackspace.com or canner46.blah.brightmail.com, you wouldn't trust my message?

rDSN does not apply to the domain on the senders address. If your envelope address is someone@example.com, I would check the SPF record for example.com. If example.com had an SPF record with a -all policy, I would refuse your email. Otherwise, it would be accepted unless it was otherwise flagged as Spam.

If your server claimed to be mail.example.com, that would trigger some actions on my side designed to determine if your server is a Spambot which it most likely would be. The lack of a valid rDNS setup would also increase your Spam spore. I have separate limits for HAM (unlikely to be not Spam), and SPAM. The messages which fall between these limits is almost entirely email from automated systems, and Spam. The person to person emails I receive almost always have correct rDNS for either or both of the IP address and name used in the HELO command.

If the DNS servers do not respond for any of the DNS lookups required to check the rDNS status of your IP address, I give a softfail. Recently, I have found this is successfully blocking a fair number of spambots. Until a few months ago this rule was rarely triggered. I believe a number of ISPs have configured there rDNS to fail for dynamic addresses ranges. If you, I appreciate their effort in reducing Spam.

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