Reverse Lookup Zone - Multiple ptr records for an IP?? 1

[blakey2]

Hi All,

We host DNS and email for multiple businesses.

mail.companyA.com --> 203.xx.yy.zz
mail.companyB.com --> 203.xx.yy.zz
mail.companyC.com --> 203.xx.yy.zz

ie.
All 3 domains resolve to same external IP

This means that we would require 3 pointer records set up for reverse dns?? (Pretty sure that this is the case to satisfy anti-spam rDNS queries).

Problem is that reverse dns lookup on 203.xx.yy.zz returns mail.companyC.com ..? (So rDNS query for company A & B would fail in any case..)

Users notice multiple rDNS entries if they receive a delivery delay notification which alert user@companyA.com that their mail has been delayed and don't need to resend -- original mail from mail.companyC.com -- etc..
-- User from companyA.com says, "Who in the hell is companyC.com and what do they have to do with my email!!"..

If this makes sense?

From what I can find on the net, multiple reverse dns records are not best practice, however are legal..

For the time being I have removed the reverse dns ptr records for company A, B & C and put in a manual entry:

mail.hosted.mycompany.com.au so user's seeing this will at least understand where the error msg relates to, however I have a nasty feeling that this will come back to bite me with anti-spam, if it requires a valid rdns entry?

Thoughts..??

THANKS

 

[blakey2]

From:

http://mxtoolbox.com/cs/blogs/mxwat...-security-can-bite-when-you-least-expect.aspx

Reverse DNS issues have expanded again...and include missing PTR (domain name) or "A" (IP address) records...multiple PTR record listings for the same IP...with other checks showing upstream host PTR records instead of the user's. Keep in mind that while these scenarios don't usually create NDRs (Non Delivery Reports), they can make it difficult to get de-listed from various RBL sites.