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I'm recently moved the email server from Company branch A to Company branch B. Branch A company is using original.com and branch B is using another.com

Scenario:

Branch A

Original.com  ( 192.0.0.1  example ip)
mail A    192.0.0.1
MX 10 mail.original.com

Branch B

another.com (182.0.0.1 example ip)

now, i have take the changes as below:

Original.com (192.0.0.1 example ip)
mail A  182.0.0.1
mx  10 mail.original.com

so, now,May I know the REVERSE DNS should define in original.com or another.com 's named.conf? By right should define the reverse DNS in original.com with 1.0.0.182.in-addr.arpa zone. is it correct?

Regards, MH

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If you want full-circle Reverse DNS, you have two choices in this situation.

OPTION A:

1.0.0.182.in-addr.arpa. PTR mail.original.com

In this situation, you would use mail.original.com as the reverse DNS record for Branch B's IP address. You also have to make sure the mail server still announces itself as mail.original.com in the SMTP banner.

OPTION B:

another.com (182.0.0.1 example ip)
mail A 182.0.0.1

original.com (192.0.0.1 example ip)
MX 10 mail.another.com

1.0.0.182.in-addr.arpa. PTR mail.another.com

With the second option, remove the A record from Branch A's DNS for the 'mail' hostname, then just direct it to mail.another.com as the MX server. At Branch B, you add the 'mail' A record to their DNS. You should also make sure the server anounces mail.another.com for its SMTP banner. Both branches will be able to retain their hostname associated with their IP address. Whether or not this is important is a company decision.

You may have thought of Option B already, I just wanted to include it in case you didn't.

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  • Hi there, thanks for your reply. I have added in the another.com. file with 1.0.0.182.in-addr.arpa. PTR mail.original.com at the bottom, but no luck Nov 25 '15 at 7:13
  • i just wonder, if we type nslookup <ip address> how we know the server name that it return is from which server? Nov 25 '15 at 7:17
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    Oh, an email server will work without reverse dns, you just might get flagged by some anti-spam solutions. If you can't send/receive at all then the problem is elsewhere.
    – Neil
    Nov 25 '15 at 7:47
  • hi @Neil yes, is working, but we want to make it perfect without go into client/vendor 's spam folder. Nov 25 '15 at 8:01
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Reverse DNS can't be configured in the named.conf file of original.com or another.com. These are forward lookup zones. The owner of the IP addresses controls the reverse lookup zone, so will need to make the changes or delegate the zone to you. Most likely this will mean a request to your hosting provider or ISP.

Your original setup of having both MX records point to the same A record is the correct configuration. Just make sure that your mail server announces its host name as mail.original.com when it makes outbound SMTP connections. As deliverability is your main concern, I also highly recommend that you setup SPF and DKIM records for your domain. These will have at least as much impact as reverse DNS records.

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  • hi, ya..thanks. i actually want to tell is dns configuration, there only put zone Nov 25 '15 at 13:53

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