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Reverse DNS/PTR

Posted on 2014-08-27
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Last Modified: 2014-08-28
Dear Experts,
I am getting a bounce back mails with error code,  "Forged hostname for XX.XX.XX.XX which resolves as srv30.vorexa.us but srv30.vorexa.us does not resolve back to XX.XX.XX.XX. Check your DNS A and PTR records. "

I found some help on line, which was this advise.

..The issue is with your Reverse DNS / Pointer Record (PTR).  You will need to contact your ISP (Internet Service Provider) and request that they configure a valid PTR that resolves to the proper IP address.
We recommend having mail.xxxxx.com configured as the RDNS for  XX.XX.XX.XX.

I contacted my ISP, who is LightPath, but they have no idea what I am talking about.  Please help.  Thank you.
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Question by:yballan
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14 Comments
 
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Assisted Solution

by:stu29
stu29 earned 1000 total points
ID: 40288166
Your email goes out through your internet connection.  Whatever IP address you have configured on your equipment is the IP address that will show up to remote servers as the originating address.  Most server nowadays do a reverse lookup on that originating IP address to minimize on spam.

You need to tell your ISP .. that they need to configure the IP address decided on above, to respond to your mail server name (srv30.vorexa.us).  This is a DNS record entry for reverse lookups.  Ask for the DNS team next time you call them, they will understand.
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LVL 41

Expert Comment

by:footech
ID: 40288193
XX.XX.XX.XX should be the public IP from which your sent mail originates.  If you only have one public IP, then so much the easier.  You should have an A record in public DNS (available to the internet) which points at that IP.  If the name of that A record is "mail.xxxx.com", then you should have a PTR record for the IP XX.XX.XX.XX which points at the name "mail.xxxx.com".  And yes, your ISP is almost always the one who will manage the PTR record, as they are the ones in control of the IP address.  At least sometimes, the A record has to be in place before they will create the PTR record.

Generally you will contact the NOC at your ISP to get the PTR record created or updated.  Some few ISPs don't allow you create PTR records, and if so, then your only option is to change ISPs.
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LVL 2

Expert Comment

by:Neil Preeper
ID: 40288707
If you can't find who to call or you think it will take some time before getting the issue fix, you can set your SMTP server to relay your e-mails through your ISP SMTP server. At least you'll have mail working properly until then.
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Author Comment

by:yballan
ID: 40290255
Dear stu29, footech, Preeper,

Thank you for your insightful advises.
I neglected to add that we use a 3rd party company, MXToolbox, as our mail filtering company.
is it their responsibility, then?
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Expert Comment

by:stu29
ID: 40290369
Does MXToolbox filter your outbound also?
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LVL 2

Expert Comment

by:Neil Preeper
ID: 40290442
You're getting this error from sending mail. Do you run an exchange server?
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LVL 41

Expert Comment

by:footech
ID: 40290554
MXToolbox, or MXLogic?  Just curious because I didn't think MXToolbox offered any mail services.
If you're using a 3rd party as a smarthost, then it would be their responsibility to have their DNS records in order.  Typically any company that offers that service is well-versed in that sort of thing.
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Author Comment

by:yballan
ID: 40290646
Yes, it is MXToolbox, which filteres inbound mails for us, as well as it takes over if our Exchange server goes down as an emergency mailboxes.
We are running MS Exchange Server 2010, but MXToolbox does not filter outbound mails.
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Accepted Solution

by:
footech earned 1000 total points
ID: 40290775
If you're not sending through MXToolbox, then it's not their responsibility.

The problem could be in one of two places, either in the A record, or the PTR record.  I already described the relationship that has to exist between these two.
Check the records yourself with nslookup.  Run the following at a command prompt (where xx.xx.xx.xx is your public IP you're sending mail from).
nslookup -q=ptr xx.xx.xx.xx 8.8.8.8
Should return the current PTR record for the IP.  Pay attention to the name.
nslookup whatever.example.com 8.8.8.8
Substitute the correct hostname for "whatever.example.com".  Is the result referencing the correct IP?

Depending on which one is incorrect, you either:
- to fix A record, do it yourself if you manage your own DNS records, otherwise contact your hosting company
- to fix PTR record, contact your ISP
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LVL 9

Expert Comment

by:stu29
ID: 40290786
@footech has answered precisely.  If you are unsure on the results of your lookups .. post them back and someone will assist.
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Author Closing Comment

by:yballan
ID: 40291071
thank you, let me just verify that ISP means whoever provides our Internet (in our case LightPath), correct?
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LVL 41

Expert Comment

by:footech
ID: 40291093
Yes.
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Expert Comment

by:graham84
ID: 40291429
Hi,

If you are not sending mail through a smarthost then it is the responsibility of the ISP to emend your PTR record.

I had this problem with British Telecom in the UK when I needed to set a PTR record. I asked for the networking team, and they sorted it out.

Once the record has been set, you can verify the record by going to http://www.wotsmyip.net and selecting "What's My Hostname" or some other similar site.
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Author Comment

by:yballan
ID: 40291703
Dear graham84,

Thank you for your advise, I requested our ISP (LightPath) and initially they acted like I was crazy, but finally got one tech support person to put through the change.  I was told that it takes at least 24 hours to propagate, so I will test it using your suggested website.
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