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Can I have 2 IPs with the same PTR Record?

For example:

122.122.122.1 with PTR Record mail.example.com.

122.122.122.2 with PTR Record mail.example.com.

Each IP-address is with a different ISP, the purpose for this is because im running a email server with one IP but here in my country sometimes the internet service providers falls and keep fall about 1-2 days , so the plan is , when one ISP falls I could use the IP from the other ISP changing the “A” record to point to the other IP.

Is this possible to have same PTR Record in two different IPs?

diya
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Jorge Enrique Garzon
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1 Answers1

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Technically you can use any hostname on a reverse DNS record, even hostnames/domains that you don't own and operate.

So in that regard there is no real obstacle.

But:

Generally it is considered a configuration error when forward and reverse DNS records don't match. See for example https://www.rfc-editor.org/rfc/rfc1912.html#section-2.1

And you mileage may vary a bit when you make the forward record for mail.example.com. a round robin one pointing to both IP-addresses.

To prevent spammers from assigning reverse DNS records from domains they don't own (to appear trusted): many spam filters will do two lookups:

  • a reverse DNS lookup of the IP-address from the remote SMTP server
  • a second lookup to see if the forward DNS record, the A record in case of IPv4 address, an AAAA in case of an IPv6 IP-address, matches reverse DNS record on that IP-address

When the two don't correlate - the spam score is increased and/or the message rejected.

It wouldn't surprise me if at some spam filters won't handle round-robin forward DNS records properly and then part of your mails will be considered spam.

diya
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