Some clarity needed please

I finally have an IP address I can set for reverse DNS for my mail servers do I need to set it to the main domain or the mail.domain.com?

On MX toolbox I get the following errors:

  • Reverse DNS does not contain the hostname
  • Reverse DNS does not match SMTP Banner

How do I set the correct SMTP banner?

I have other domain names that I host (personal sites), would I get the same error for for these when using the other mail domain’s?

Thank you in advance, trying to learn more about how it works.

By default, the SMTP banner showed by Exim is the hostname of your server. You can view it easily connecting to your mail server:

$ telnet mail.yourdomain.tld 25
Trying 203.0.113.1...
Connected to mail.yourdomain.tld.
Escape character is '^]'.
220 here.you-will-see-the.hostname  <-- this is the hostname you must use for the reverse dns

Edit: if you don’t have telnet installed and don’t want to install it, you can also use openssl:

$ openssl s_client -connect mail.yourdomain.tld:465 -quiet 2>/dev/null
220 here.you-will-see-the.hostname  <-- this is the hostname you must use for the reverse dns

If you use the hostname Exim is showing, you won’t have any problem.

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Thank you very much.

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