Regular DNS turns a name into an address. Reverse DNS does the opposite: it takes an IP address and finds the name assigned to it. It matters most for email, where receiving servers use it to decide whether a sender looks legitimate, but it also helps when reading server logs, tracing where traffic comes from and troubleshooting network problems. The tool above finds the reverse DNS name for any IPv4 or IPv6 address, checks that the name points back to the same address and flags names that look generic.

What Reverse DNS Is

Every public IP address can have a PTR record, short for pointer record, that names it. When you look up an address such as 8.8.8.8, the lookup goes to a special part of DNS called in-addr.arpa, where the address is written backwards, and returns a name, in this case dns.google. IPv6 addresses work the same way under ip6.arpa, with each hexadecimal digit reversed.

A PTR record is optional, and many addresses have none. Others have a generic name created by the internet provider that includes the address itself, which tells you who owns the address but little else.

What This Tool Checks

Enter an IP address to look up its PTR record directly, or enter a hostname to check every address it points to. For each address, the tool reports:

• The PTR record, or that none is set
• Whether the name points back to the same address, a test called forward-confirmed reverse DNS
• Whether the name looks like a generic one assigned by an internet provider
• Whether it is an IPv4 or IPv6 address

When something needs fixing, a What to Fix box explains the change and who can make it. For IPv4 addresses, a button takes you straight to the Email Blacklist Check for the same address.

Why Reverse DNS Matters for Email

Mail servers receive huge amounts of spam from infected home computers and hijacked servers, and reverse DNS is one of the cheapest ways to filter it. Before accepting a message, many servers look up the PTR record of the address that connected. If there is none, or the name is clearly a home connection, the message is far more likely to be rejected or sent to spam.

Large providers such as Gmail and Outlook require senders to have valid reverse DNS that matches a forward record. If you run your own mail server, or send from a virtual server or a dedicated address, correct reverse DNS is one of the basic requirements, along with SPF, DKIM and DMARC.

Forward-Confirmed Reverse DNS Explained

Anyone who controls an address can set its PTR record to any name, including one they do not own. To guard against that, servers check the other direction too. They take the name from the PTR record, look up its address in regular DNS and confirm it matches the original address. When both directions agree, the setup is called forward-confirmed reverse DNS, often shortened to FCrDNS.

If the PTR record says mail.example.com but mail.example.com points somewhere else, or does not resolve at all, the check fails. The fix is usually an A record, or an AAAA record for IPv6, in your own domain’s DNS that points the name to the right address.

Who Controls Reverse DNS

This is the part that confuses most people. Your domain’s DNS settings control names under your domain, but the PTR record for an address belongs to whoever owns the address block. That is usually your hosting company, cloud provider or internet provider, not your domain registrar.

Most hosting and cloud providers let you set the PTR record yourself, often in the server’s network or IP settings. Others ask you to open a support request. Home internet connections usually cannot have a custom PTR record at all, which is one reason running a mail server from home rarely works well.

How to Read Your Results

For a single address, the large text at the top shows its reverse DNS name. Green means the name exists, points back to the same address and looks like a proper name. Amber means one of those checks failed, and the line underneath explains which one. For a hostname, the top line says how many of its addresses have reverse DNS.

Each detail has a colored dot. The Points Back row shows what the name resolves to, so you can see at a glance whether it matches. The Name Type row marks names that look generic, such as ones that include the address itself or words like dynamic, pool or dsl.

How to Fix Missing or Wrong Reverse DNS

Start by deciding on the name. For a mail server, use the same name it uses to introduce itself when sending mail, such as mail.example.com. Then set it in two places. First, in your domain’s DNS, add an A record for that name pointing to the server’s address, plus an AAAA record if it has an IPv6 address. Second, in your hosting or cloud provider’s control panel, set the PTR record for the address to that name, or ask their support team to do it.

Changes can take from a few minutes to a day to appear, depending on the provider. Run the lookup again afterward to confirm both directions match. If you send email from this address, check it on the Email Blacklist Check as well.

Other Uses for Reverse DNS

Reverse DNS is not only for email. System administrators use it to make server logs readable, since a name like crawl-66-249-66-1.googlebot.com says far more than a bare address. It is also a common way to confirm that a visitor claiming to be a search engine crawler really is one, because the major search engines publish the names their crawlers use and set forward-confirmed reverse DNS for them.

Network tools such as traceroute use reverse DNS to label each hop along a route, which often reveals the provider and city of each router. Security teams use it to get a quick sense of who owns an address before digging further.

Your Lookups Stay Private

We do not keep a record of the addresses or names you look up, or anything about who looked them up. Each result is held for ten minutes so a repeated lookup loads quickly, then deleted. Private and reserved addresses, such as those used inside home and office networks, cannot be looked up because they have no public reverse DNS.