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How to configure Reverse DNS, PTR and MX records for private email server behind Comcast Static IP

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Martinator
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How to configure Reverse DNS, PTR and MX records for private email server behind Comcast Static IP

Hello, I have some questions on how to set-up Reverse DNS, PTR and MX records for our private Exchange email server sitting behind a Comcast Static IP address.

 

We run our own Exchange server on a private network behind static IP address: 70.91.104.193.  Our domain is www.estarmail.com and mail.estarmail.com for email. I have registered these domains and set up Reverse DNS, PTR and MX records at REGISTER.COM our registrar.

 

When I go to DNSQUERY.COM I get no results for A, CNAME, MX and TXT queries. The DNS and PTR query properly return estarmail.com for my IP. The reverse DNS query returns an undefined (???) PTR to my domain. The WHOIS query returns Comcast Business Communications, LLC.

 

What can I do to get the various missing or incorrect DNS records set up so they will resolve properly to our static IP and domain?

 

Martin Kultermann
eStar Communications
Office:  +1 (773) 697-8283
Cell:     +1 (847) 372-2381

Email:  Martinator@eStarMail.com

Accepted Solution

Re: How to configure Reverse DNS, PTR and MX records for private email server behind Comcast Static

A domain registry like register.com is only authoratative for forward records like A records and MX records.  You can only setup PTR records with the hoster of the IP address block - in this case Comcast.

 

The by the book process is contact Comcast on the phone Mon-Fri 8-5pm Eastern time.

 

Incidentally your PTR isn't correct.   Take a look at the following:

 

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\tedm>nslookup
Default Server:  UnKnown
Address:  172.16.1.13

> set type=mx
> estarmail.com
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
estarmail.com   MX preference = 0, mail exchanger = mail.estarmail.com

estarmail.com   nameserver = dns142.a.register.com
estarmail.com   nameserver = dns167.b.register.com
estarmail.com   nameserver = dns223.c.register.com
estarmail.com   nameserver = dns249.d.register.com
mail.estarmail.com      internet address = 70.91.104.193
dns142.a.register.com   internet address = 216.21.231.142
dns167.b.register.com   internet address = 216.21.232.167
dns223.c.register.com   internet address = 216.21.235.223
dns249.d.register.com   internet address = 216.21.236.249
> set type=a

> mail.estarmail.com
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
Name:    mail.estarmail.com
Address:  70.91.104.193

> set type=ptr
> 70.91.104.193
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
193.104.91.70.in-addr.arpa      name = estarmail.com

------>>>>>>>>>>>>>>>>>>>>>>>>>>^^^^^^^^^^^^^

(should be mail.estarmail.com)

91.70.in-addr.arpa      nameserver = dns104.comcast.net
91.70.in-addr.arpa      nameserver = dns102.comcast.net
91.70.in-addr.arpa      nameserver = dns103.comcast.net
91.70.in-addr.arpa      nameserver = dns105.comcast.net
91.70.in-addr.arpa      nameserver = dns101.comcast.net
dns101.comcast.net      internet address = 69.252.250.103
dns101.comcast.net      AAAA IPv6 address = 2001:558:fe23:8:69:252:250:103
dns102.comcast.net      internet address = 68.87.85.132
dns102.comcast.net      AAAA IPv6 address = 2001:558:1004:7:68:87:85:132
dns103.comcast.net      internet address = 68.87.76.228
dns103.comcast.net      AAAA IPv6 address = 2001:558:1014:c:68:87:76:228
dns104.comcast.net      internet address = 68.87.68.244
dns104.comcast.net      AAAA IPv6 address = 2001:558:100a:5:68:87:68:244
dns105.comcast.net      internet address = 68.87.72.244
dns105.comcast.net      AAAA IPv6 address = 2001:558:100e:5:68:87:72:244
>

 

Forward and reverse records only exist for hostnames not domains.

 

A domain (estarmail.com) can have a MX record and it can have an A record but the MX

record is only used for routing mail.  The A record is not.   CNAME records are not used

for routing mail at all.   Setting a PTR  (reverse DNS) record to point to a domain instead of

a hostname is nonsensical.

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2 REPLIES
Forum Contributor

Re: How to configure Reverse DNS, PTR and MX records for private email server behind Comcast Static

A domain registry like register.com is only authoratative for forward records like A records and MX records.  You can only setup PTR records with the hoster of the IP address block - in this case Comcast.

 

The by the book process is contact Comcast on the phone Mon-Fri 8-5pm Eastern time.

 

Incidentally your PTR isn't correct.   Take a look at the following:

 

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\tedm>nslookup
Default Server:  UnKnown
Address:  172.16.1.13

> set type=mx
> estarmail.com
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
estarmail.com   MX preference = 0, mail exchanger = mail.estarmail.com

estarmail.com   nameserver = dns142.a.register.com
estarmail.com   nameserver = dns167.b.register.com
estarmail.com   nameserver = dns223.c.register.com
estarmail.com   nameserver = dns249.d.register.com
mail.estarmail.com      internet address = 70.91.104.193
dns142.a.register.com   internet address = 216.21.231.142
dns167.b.register.com   internet address = 216.21.232.167
dns223.c.register.com   internet address = 216.21.235.223
dns249.d.register.com   internet address = 216.21.236.249
> set type=a

> mail.estarmail.com
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
Name:    mail.estarmail.com
Address:  70.91.104.193

> set type=ptr
> 70.91.104.193
Server:  UnKnown
Address:  172.16.1.13

Non-authoritative answer:
193.104.91.70.in-addr.arpa      name = estarmail.com

------>>>>>>>>>>>>>>>>>>>>>>>>>>^^^^^^^^^^^^^

(should be mail.estarmail.com)

91.70.in-addr.arpa      nameserver = dns104.comcast.net
91.70.in-addr.arpa      nameserver = dns102.comcast.net
91.70.in-addr.arpa      nameserver = dns103.comcast.net
91.70.in-addr.arpa      nameserver = dns105.comcast.net
91.70.in-addr.arpa      nameserver = dns101.comcast.net
dns101.comcast.net      internet address = 69.252.250.103
dns101.comcast.net      AAAA IPv6 address = 2001:558:fe23:8:69:252:250:103
dns102.comcast.net      internet address = 68.87.85.132
dns102.comcast.net      AAAA IPv6 address = 2001:558:1004:7:68:87:85:132
dns103.comcast.net      internet address = 68.87.76.228
dns103.comcast.net      AAAA IPv6 address = 2001:558:1014:c:68:87:76:228
dns104.comcast.net      internet address = 68.87.68.244
dns104.comcast.net      AAAA IPv6 address = 2001:558:100a:5:68:87:68:244
dns105.comcast.net      internet address = 68.87.72.244
dns105.comcast.net      AAAA IPv6 address = 2001:558:100e:5:68:87:72:244
>

 

Forward and reverse records only exist for hostnames not domains.

 

A domain (estarmail.com) can have a MX record and it can have an A record but the MX

record is only used for routing mail.  The A record is not.   CNAME records are not used

for routing mail at all.   Setting a PTR  (reverse DNS) record to point to a domain instead of

a hostname is nonsensical.

Martinator
Visitor

Re: How to configure Reverse DNS, PTR and MX records for private email server behind Comcast Static

Thank you, I have updated the PTR record at REGISTER.COM and opened a ticket at Comcast.

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