Question 1

What is reverse DNS?

Accepted Answer

It maps an IP address back to a hostname, the opposite direction of normal DNS. The lookup happens via special PTR records in the .arpa zones.

Question 2

How do I check PTR records?

Accepted Answer

Paste the IP into the box and click Look up PTR. We return every name the address resolves to (often just one).

Question 3

Why is reverse DNS important for email?

Accepted Answer

Most mail servers reject inbound mail from IPs without a valid PTR. Setting one that matches your sending hostname is one of the cheapest deliverability wins.

Question 4

Can I set a PTR myself?

Accepted Answer

Only the owner of the IP block can. For cloud servers, your provider exposes a 'reverse DNS' field in their console; for on-prem, contact your ISP/colo.

Question 5

Why doesn't my IP have a PTR?

Accepted Answer

It's never been set. ISPs sometimes publish a generic name like 'pool-1-2-3-4.example-isp.net'; cloud providers leave it blank by default.

Question 6

Does reverse DNS work for IPv6?

Accepted Answer

Yes — via the .ip6.arpa zone. PTR records work the same way; the hex nibbles of the address are reversed and joined with dots.

Question 7

What's the difference between PTR and A records?

Accepted Answer

An A record points a name to an IP (forward). A PTR points an IP to a name (reverse). They're stored in different zones and don't update each other automatically.

Question 8

How do I fix "no PTR" warnings?

Accepted Answer

Set the PTR in your hosting provider's console to match the hostname you send mail from. Then publish a matching A record so forward and reverse agree.

Question 9

Can a PTR point to multiple names?

Accepted Answer

Technically yes, but most software (especially mail servers) only looks at the first one. Stick to a single canonical PTR per IP.

Question 10

Is reverse DNS the same as WHOIS?

Accepted Answer

No. WHOIS tells you who registered an IP block or domain. Reverse DNS only tells you what hostname the IP currently resolves to.