Exact purpose of /etc/mail_reverse_dns file?

Valetia

• January 17, 2015 15:29

What is the exact purpose of the following file? /etc/mail_reverse_dns There is some brief mention of it at the bottom of the following page:

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  cPanelMichael

  • January 19, 2015 14:36

  Hello :) Yes, it's referenced in the documentation URL you provided: The /etc/mail_reverse_dns file This file controls the domains that are associated with the IP addresses from which mail should send. Your file should be similar to the following example: 192.168.0.2: example.com 192.168.0.2: sub.example.com 192.168.0.3: example.net 192.168.0.3: addon.example.net Note: This file must contain an entry for your server's main hostname and primary IP address. Make certain to use only valid IP addresses that are publicly accessible via the Internet.
  You don't have to make any modifications to this file if you are not modifying the IP addresses used by your domain names for sending email. Thank you.

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  Valetia

  • January 19, 2015 17:20

  Thank you for your reply. The issue is that the documentation URL is rather vague on the purpose of the file. What (if anything) does cPanel and/or Exim do with that file exactly? The file name 'mail_reverse_dns' implies that it has something to do with the PTR. However, as per the documentation snippet that you've quoted, you can see that multiple domains are assigned to each IP in that example, which is not a very common type of PTR setup. Commonly, an IP is assigned to only a single hostname via a PTR, particularly one used for email purposes. In addition, PTRs are usually managed via the data center/server provider's website. Surely those settings are what the external mail servers would see, rather than what's in the /etc/mail_reverse_dns file? We currently customize our own /etc/mailips and /etc/mailhelo files, but we are unsure if we should leave the /etc/mail_reverse_dns alone. If we were to follow the example in that documentation snippet, and assign multiple domains to each IP, then there would be hundreds or thousands of lines in that file, since there are that many domains/subdomains being hosted per server. We would also need to add new lines to the file each time a user adds a domain or subdomain. Does that seem right? Also, none of those hundreds or thousands of lines would actually match up with the actual PTR entries as configured via the data center/server provider's website, since only a single mail server hostname is assigned to each IP over there. Please advise - thanks in advance!

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  cPanelMichael

  • January 28, 2015 14:49

  The following post should help answer this question: /etc/mail_reverse_dns file Thank you.

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