When sending email it’s a best practice that your sending ips reverse and forward resolutions match.
When looking up IPv4 addresses you use a special domain called in-addr.arpa so if you want to know the ptr of 8.8.4.4 just run this
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nslookup -q=ptr 4.4.8.8.in-addr.arpa //OR THIS SHORTHAND nslookup -q=ptr 8.8.4.4 Non-authoritative answer: 4.4.8.8.in-addr.arpa name = google-public-dns-b.google.com |
See the name = in the answer, that’s the PTR not to see if we have a confirmed forward and are good to go we need to see if the domains A-record match the IP we looked up. Run this
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nslookup -q=a google-public-dns-b.google.com Non-authoritative answer: Name: google-public-dns-b.google.com Address: 8.8.4.4 |
See the Address part in the answer it matches the ip we checked PTR on. That means that they are matching.
ktnxbye!