The Community Forums

Interact with an entire community of cPanel & WHM users!
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Exact purpose of /etc/mail_reverse_dns file?

Discussion in 'E-mail Discussions' started by Valetia, Jan 17, 2015.

  1. Valetia

    Valetia Well-Known Member

    Joined:
    Jun 20, 2002
    Messages:
    207
    Likes Received:
    1
    Trophy Points:
    18
    cPanel Access Level:
    Root Administrator
  2. cPanelMichael

    cPanelMichael Forums Analyst
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    30,854
    Likes Received:
    676
    Trophy Points:
    113
    cPanel Access Level:
    Root Administrator
    Hello :)

    Yes, it's referenced in the documentation URL you provided:

    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.
     
  3. Valetia

    Valetia Well-Known Member

    Joined:
    Jun 20, 2002
    Messages:
    207
    Likes Received:
    1
    Trophy Points:
    18
    cPanel Access Level:
    Root Administrator
    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!
     
  4. cPanelMichael

    cPanelMichael Forums Analyst
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    30,854
    Likes Received:
    676
    Trophy Points:
    113
    cPanel Access Level:
    Root Administrator

Share This Page