Liway IP has no PTR record

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Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 2:25 pm

Hi, I just noticed that Liway's mail server IP address 72.249.77.237 does not have an PTR record at all.

Consequently there is a risk that some remote mail servers on the Net may reject emails sent out from Liway's mail server, or perhaps consider the emails to be suspicious, as a result of this. I know for a fact that some spam filters like SpamAssassin can assign spam-points to an email if it comes from an IP address without a PTR record.

Any chance you could add a PTR record there?!

Thanks!
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Re: Liway IP has no PTR record

Postby Max » Tue Mar 13, 2012 2:27 pm

I know what a PTR record is; and indeed there should be one as I recall adding it. If it does not exist that is a bit of a shock to me :shock:

Allow me to check.
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Re: Liway IP has no PTR record

Postby Max » Tue Mar 13, 2012 2:30 pm

I just checked, and the record is in place for liway.com to 72.249.77.237 - can you link me to what is telling you it does not exist?

Edit: It's definitely showing up on a DNS lookup:

http://network-tools.com/default.asp?pr ... =liway.com

liway.com TXT v=spf1 ip4:127.0.0.1 ip4:72.249.77.237 ip4:72.249.105.73 a mx ptr ?all 14400s


Are you having issues with your emails being blocked?

Further edit: I added this record quite a long time ago, since then it seems the formal PTR record tag is used? I added a ptr record in this new manner (while keeping the old just in case), I'll be interested to see if it's correct once the records propagate :ugeek:
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Re: Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 2:49 pm

I believe you're looking at the 'A' record for liway.com which points to 72.249.77.237. This 'A' record does exist and is correct.

However, I'm referring to the PTR record (also called reverse DNS) of 72.249.77.237. This is a DNS record attached to the IP address, not attached to the domain name. Normally it's set by the internet provider which owns or manages the IP address itself.

Currently there is no PTR record for 72.249.77.237. I've confirmed this via online DNS lookup tools such as the one at http://www.dnsqueries.com/en/reverse_lookup.php as well as by doing an nslookup on my own computer.

Furthermore, I'm running my own private mail server here, and it also reports that emails received from 72.249.77.237 have no PTR record.

In comparison, you appear to have another IP address which is 72.249.105.73 and that IP address does have a PTR record (you can confirm that at http://www.dnsqueries.com/en/reverse_lookup.php).

Hope that helps! :)
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Re: Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 2:54 pm

Update: regarding the tool at http://network-tools.com, you're doing a lookup there on your domain name, liway.com, which won't tell you anything about the PTR record. The PTR record belongs to the IP, not the domain name.

If you enter your IP into the search field at http://network-tools.com you'll see that the results say "No host name is associated with this IP address or no reverse lookup is configured."

A PTR record isn't somthing that you'll be able to add yourself to your liway.com DNS settings. It needs to be added by the provider/company that is responsible for your IP address (obviously I don't know who that is).

SpamAssassin running on my own mail server is currently assigning several spam-points to emails from your server (including the notification emails I'm getting from this forum) as a result of this. So it's very likely going to be affecting other emails which your server sends out, to some degree or other. :)
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Re: Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 2:59 pm

SpamHaus, the highly-regarded anti-spam blacklist, has some comments on the importance of having a PTR record (A.K.A "rDNS"), in their FAQ at http://www.spamhaus.org/faq/section/ISP ... Issues#128.

Amongst other things, they explain:
* Publishing proper rDNS for statically assigned IPs - and in particular for those corresponding to proper mail servers - greatly reduces the likelihood that other networks will block those servers by mistake, thinking that their IP belongs to residential dynamic space.
* Moreover, some networks are refusing mail from IP addresses without rDNS defined.

More info at http://en.wikipedia.org/wiki/Reverse_DNS_lookup.
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Re: Liway IP has no PTR record

Postby Max » Tue Mar 13, 2012 3:14 pm

This is all quite strange and intriguing. 72.249.105.73 and 72.249.77.237 both belong to our server and they are both in the TXT record I quoted above (which again was added eons ago). Our DC has also put a reverse DNS on 72.249.77.237 for our hostname equally long ago. So this being an issue now (believe me I've verified the existence of the PTR record after it was added) is most inexplicable.

I will remove the other IP address (it isn't actually in use right now) from the TXT entry to ensure it cannot be responsible, and check again in 4 hours (well it will be more as I'm about to go to bed); following that I'll contact our DC.

jfairbrass wrote:A PTR record isn't somthing that you'll be able to add yourself to your liway.com DNS settings. It needs to be added by the provider/company that is responsible for your IP address (obviously I don't know who that is).


Yes, though aren't there are two elements to it? Ie. it must be added by the ISP (in our case, our datacenter) and in the domain's DNS records. At least this is/was my understanding. Otherwise a lot of stuff I have read in the past makes no sense :?:
That would not be new though :mrgreen:
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Re: Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 3:29 pm

Removing the IP from that TXT record won't have any effect at all on the PTR record, I can assure you! :) That TXT record is used as your SPF record, and is part of the DNS settings of your domain name (liway.com) and not your IP address.

You could view it like this, with the various DNS settings that belong to your domain name:

liway.com => TXT => v=spf1 ip4:127.0.0.1 ip4:72.249.77.237 ip4:72.249.105.73 a mx ptr ?all
liway.com => MX => 0, liway.com
liway.com => A => 72.249.77.237
liway.com => NS => ns1.liway.com

...and so on. Those are all DNS records for liway.com. But a PTR record cannot appear there, because a PTR record belongs to the IP address. the PTR record maps the IP to the hostname - they're essentially the opposite of an 'A' record, which maps the hostname to its IP address. Therefore:

72.249.77.237 => PTR => tesla.liway.com (or whatever you set it to)

The only way to edit or change the PTR record is to ask whoever owns the IP to do it for you - eg. your upstream provider.

Believe me, most people struggle to get their heads around PTR records - even when I deal with my own ISP's technicians, who of all people should understand this stuff, they frequently have no idea what it is, or they wrongly assume it's something to do with the DNS records of my domain rather than of their IP address. :)
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Re: Liway IP has no PTR record

Postby jfairbrass » Tue Mar 13, 2012 3:37 pm

Max wrote:Yes, though aren't there are two elements to it? Ie. it must be added by the ISP (in our case, our datacenter) and in the domain's DNS records. At least this is/was my understanding. Otherwise a lot of stuff I have read in the past makes no sense :?:
That would not be new though :mrgreen:


Well, kinda. If you view the PTR record as being basically the opposite of the A record, then yeah there are two parts: the A record and the PTR record. But really they are quite independent of each other, and you can have either one without the other.

However, common practice - especially for a static IP address like yours, which is being used for a mail server - is to have your mail server's domain name (hostname) point to the IP via an A record, and then have the IP address point back to the domain name via the PTR record. That's what the FAQ at SpamHaus was getting at. So you'd do something like this:

liway.com => A => 72.249.77.237
72.249.77.237 => PTR => liway.com

So you would add the A record, and your DC would add the PTR record. If your DC did add this in the past, then they appear to have since removed it. :(
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Re: Liway IP has no PTR record

Postby Max » Wed Mar 14, 2012 2:23 am

Alrighty, now it should be settled.

Thanks for bringing this to our attention!
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Re: Liway IP has no PTR record

Postby jfairbrass » Wed Mar 14, 2012 6:27 am

Yup, I can see the PTR record now - super! :)
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