# Anyone know about PTR records?



## hockey97 (Apr 12, 2012)

Hi, my question is directly with DNS servers. I would like to know how exactly to setup a PTR record? Do I need to contact my ISP to made me a PTR record? 
If you don't know what I am talking about. PTR is simply a reverse domain lookup record. 
So if you then take the domain name then grab the persons IP  address it should then give me the same domain name.

For example:

Normal DNS  A record :  Domain ---> IP address. 
Converts domain name to IP.

PTR record :  IP ----> Domain 
Converts IP address back into domain name.

PTR record by default:  IP ----> Domain_Of_ISP   
So the domain name it grabs would be of your ISP's domain name. 

Now AOL and many popular e-mail providers would do this to lable spam they think that if your ISP points towards a domain name  that isn't of your own domain name then you be a spammer. 

So, my e-mails which are important would get tossed into the spamming list on AOL.com 
It's because my PTR record points to my Internet providers domain name. 
I never experience setting up my own stuff from ground up. I would like to know if it's possible to just tell my ISP to change this. I am not 100% sure. Just asking here if anyone went thru it or knows something that went thru this.


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## Mormegil (Apr 12, 2012)

If this is a home server, your ISP will probably only set this up for you if you have a static IP address assigned to you. If so, then yes, just email their tech department with the requested mappings.

For a hosted server, the same thing applies, you should just have to submit a request to their tech department to have the entries created. Some will even delegate control of your subnets to your own DNS servers, allowing you to create your own forward and reverse mappings. My home ISP (Verizon) will do this, but only with a /28 or larger.


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## _martin (Apr 12, 2012)

Who is managing IP address/range in question? If you're not managing the range, you should contact ISP (==owner) to change your PTR (typical for many hosting providers, etc.).

If you are the owner or you are managing it, the PTR record is set the same way as A record - you define the proper zone, header and the record in it. Usually localhost is set by default in any DNS server, you can get the idea from there.


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## hockey97 (Apr 17, 2012)

No, I have a small office. The ISP manages the  IP ranges. I already pay for 1 static IP address. It's just that my mail that I send to clients are actually being tossed in spam folders or gets blocked totally because the reverse DNS lookup shows my ISP and not my own domain name.


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## DutchDaemon (Apr 18, 2012)

That is likely not the problem. Most spam filters don't like it when _reverse_ DNS (PTR) doesn't match forward DNS (A), NOT the other way around. If your IP (the IP that connects to a mailserver) resolves to ip123.isp.com, but ip123.isp.com does not exist, or resolves to a different IP, then spam filters may get nervous. This problem is more common than you think. Your own domain name or DNS records have much less to do with this. Check out the DNS record for your IP address (with *dig -x*), then check whether that hostname (if there _is_ a hostname at all, which is also a common problem) resolves to that same IP address. If not, the ISP should make sure A and PTR records exist and match.

Addendum: I checked out the IP address you use to connect to this forum. The IP has a valid PTR record, but when I look up the hostname presented by that PTR record, it does not return an A record, in other words: it does not exist. That is the problem. Your ISP must fix that and provide a matching A record.


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## aa (Apr 18, 2012)

Not just matched A/PTR record, today most of them need a valid MX as well. Many public sites such as yahoo or google also requires that an incoming email is DKIM signed, otherwise it will be considered as spam.

You can simply ask your upstream provider to fix the lookup-reverse PTR record, also add MX and DKIM selector in DNS:


```
your.domain.name.
  IN A your-IP-address
  IN MX 10 your-mail-IP-address

s1._domainkey.your.domain.name.
  IN TXT "your-DKIM-resouce-records"
```


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## hockey97 (Apr 19, 2012)

DutchDaemon said:
			
		

> That is likely not the problem. Most spam filters don't like it when _reverse_ DNS (PTR) doesn't match forward DNS (A), NOT the other way around. If your IP (the IP that connects to a mailserver) resolves to ip123.isp.com, but ip123.isp.com does not exist, or resolves to a different IP, then spam filters may get nervous. This problem is more common than you think. Your own domain name or DNS records have much less to do with this. Check out the DNS record for your IP address (with *dig -x*), then check whether that hostname (if there _is_ a hostname at all, which is also a common problem) resolves to that same IP address. If not, the ISP should make sure A and PTR records exist and match.
> 
> Addendum: I checked out the IP address you use to connect to this forum. The IP has a valid PTR record, but when I look up the hostname presented by that PTR record, it does not return an A record, in other words: it does not exist. That is the problem. Your ISP must fix that and provide a matching A record.



I currently host my own 2 domain names. I host my own mail servers. So is it possible to make two PTR records? *T*he current PTR record is using my ISP domain name with the word static meaning my IP is static. I don't understand what you mean by A record? *M*y domain names are on another DNS server with an A record and a MX record. So when I call up my ISP I would need to request them to make an A record for my IP address?


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## DutchDaemon (Apr 19, 2012)

You have to understand that _your_ domains and your own DNS server(s) play absolutely no role here. It is your ISP that provides a name for your public IP address (a PTR record, or "reverse lookup" record), and, conversely, an IP address for that name (an A record, or a "forward lookup" record). Both records are hosted on your ISP's authoritative DNS servers (the A record under their own domain name's zonefile, the PTR record under the corresponding in-addr.arpa zone file). Right now, only the PTR record has been put in place; in other words, your public IP address resolves to a hostname (*dig -x your.ip.addr.es*). But that same hostname does not resolve back to the IP address (*dig A your.public.hostname*), so that hostname does not have a corresponding A record that matches the PTR record. 

Yes, your ISP needs to fix that.


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## throAU (Apr 19, 2012)

As DutchDaemon said, the PTR records are under the control of the IP net-block owner.  If you need a public pointer record setup, contact your ISP, they are the only ones who can fix this.

If you have a business grade service, this shouldn't be a problem.  If you don't then you may need to pay for one before they will do a PTR record for you.

And yes, this is a common mail server configuration issue - so common that spam filters don't generally use a forward/reverse DNS record mis-match as definite spam, it just slighty weights the spam score towards spammy.


edit:
No you can't have 2 PTR records for the same IP.  Well, you could maybe configure that in the zone file, but it would defeat the purpose of using PTR records entirely (purpose being to get a single hostname back for an IP) and such a configuration would be "broken".


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## hockey97 (Jul 14, 2012)

I was told that the   PTR record is the same as an A record. I was told that I  can 
make many ptr records for a single ip but it's better practice to have another ip address for the other domain.This monday I be giving my ISP a call. Ya, I got business graded Internet.So not sure if they will charge me extra for these ptr records.


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## Mormegil (Jul 15, 2012)

A PTR record is not the same as an A record.

An A record maps a hostname to an IP address.


```
foo.bar.com -> 0.0.0.0
```

A PTR record maps an IP address to a hostname.


```
0.0.0.0 -> foo.bar.com
```

It's common practice to have multiple A records for a single IP where needed. On the other hand, while it's possible to have multiple PTR records, it's generally not recommended to do so unless absolutely necessary and if you know exactly what you're doing.


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