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We have an MS Exchange deployed on an ISP network in our office. Currently, when a mail recipients' server would try to lookup an IP of the server, from which it is receiving a message, that is marked as, for example, from ourdomain.com, it doesn't find a DNS PTR record.

I am to ask a provider to add one to the DNS Server, that is covering the zone, on which our IP is located.

We are sending messages as senders from two domains. Can I ask a provider to set up a DNS PTR to return two domains on one IP?

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2 Answers 2

up vote 4 down vote accepted

You can have multiple ptr records, however you will only read the first returned. In practice this can give quite some problems. So you should stick to just one PTR record for your IP.

When sending an email, the receiving server only cares if you are RFC compliant (Sending FQDN resolves to IP and IP's PTR resolves back to FQDN). As long as they all resolve, your server will be happy.

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My real situation is: I am sending from support@komplus.ua. komplus.ua resolves as an IP. The recieving server looks up that IP, and gets a kerosgroup.com domain in return (first one from the ISP DNS), which isn't the same as komplus.ua. And here I get a problem, right? –  Maxim V. Pavlov Feb 15 '12 at 13:14
    
Normally it shouldn't as long as any ptr record is defined for an IP your mailserver shouldn't reject it. I think you are bussy with a spamfilter correct ? I've ran into this too and in my experience this should be enough. –  Lucas Kauffman Feb 15 '12 at 13:21
    
Yep, one of the email servers thinks I am spamming since no PTR is defined at all. Thanks for clearing it out for me! –  Maxim V. Pavlov Feb 15 '12 at 13:30
    
@MaximV.Pavlov Some sites check that the forward (A) and reverse (PTR) DNS entries match -- If you have multiple PTRs this can lead to intermittent strangeness (getting marked as spam). One PTR record per IP (returning the same name as the "most important" A record, and in the case of mail servers both of them matching the SMTP Greeting's machine name that your server sends in its HELO/EHLO) is the Appropriately Paranoid way to go :-) –  voretaq7 Feb 15 '12 at 14:54

You have to have one PTR for sender-IP, and name of PTR must resolve to IP from PTR

If your emitter for komplus.ua is same as MX, than

Quering 8.8.4.4 for {mail.komplus.ua.,ANY}
Received answer from 8.8.4.4
  Not authoritative

Answers for mail.komplus.ua.:
  -> [A] 91.221.211.130 

means, that

Quering 8.8.4.4 for {130.211.221.91.in-addr.arpa.,PTR}
Received answer from 8.8.4.4
  Not authoritative
  Domain name doesn't exist

is bad, because 130.211.221.91.in-addr.arpa. must be resolvable to mail.komplus.ua

and EHLO parameter also in best case mail.komplus.ua., but can be any other name, which in IN A request return 91.221.211.130

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