Reverse DNS when sending mail from multiple IP/subdomains

domain-name-systememailreverse-dns

I have site example.com and I want to set an external mail server m1.example.com , most whitelists like AOL requires reverse DNS for all IPs, but in order to fetch the bounces properly I will be sending mail like this, return path and from being different domains:

return-path noreply@m1.example.com
from: noreply@example.com

So I am unsure if the reverse DNS of m1 IP should match the m1.example.com or just example.com

Thank you.

Best Answer

Receiving mail servers check none, one, many or all of the following:

  1. Is the HELO name equal to the hostname (A record)?
  2. Is PTR of the IP equal to the A record of the hostname (hostname ==(PTR)==> IP ==(A)==> hostname)?
  3. Is the IP part of the provided SPF record?
  4. Does the sender's domain have at least one MX record? Which doesn't have to match IP/hostname.

Receiving mail servers that check if the sending server is also the MX server are badly configured and should be eliminated from the Internet.

Same goes for servers that check if the hostname is equal to the domain name of the mail. Look at Google where you can send mail with (almost) any domain whereas their hostname always contains google.com.

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