How to Find Out Who Runs a Domain Extension (And Whether It Has RDAP)

To find out who runs a domain extension, read its record in IANA's root zone database. The TLD registry lookup does it through IANA's RDAP service for up to 100 extensions a run (500 after a free Google sign-in). Each TLD shows its sponsoring organisation, the technical contact's organisation, its type, the year it entered the root, DNSSEC and its RDAP server.

Only organisation names are shown. Contact people and addresses are left out.

The by-hand way

1. Open IANA's Root Zone Database and search for the extension.
2. Read the sponsoring organisation and the administrative and technical contacts.
3. Check IANA's RDAP bootstrap file to see whether the TLD has an RDAP service and where it is.

Step 1: paste the extensions

Paste extensions (.io), domains (acme.co.uk) or URLs, one per line. Each line is reduced to its last label and repeats are merged. Up to 100 a run without an account, 500 after a free Google sign-in.

Step 2: run the lookup

Each TLD is looked up once in IANA's root zone RDAP service.

Step 3: read each row

Mark	What it means
Has RDAP	The registry publishes an RDAP service, shown with its address
No RDAP	No RDAP service in IANA's bootstrap file
Not a TLD	The last label is not in the root zone
Lookup failed	IANA did not answer, so try again

The technical contact's organisation is often a back-end operator that runs the registry systems for the sponsor, which is why one TLD can show one company as sponsor and another as technical contact.

Why RDAP support matters

It decides what a domain lookup can tell you. Under a TLD with RDAP, a WHOIS lookup or domain age check can read the registration date and registrar directly from the registry. Under one without, a bulk tool can only say it could not tell. That is why some domains show unknown in status code and transfer checks. For what RDAP does and does not reveal, see what WHOIS privacy hides, and for choosing an extension to send from, the best TLD for cold email domains.

What this check cannot do

• IANA's records name the sponsor and contacts. They do not include prices, eligibility rules or registrar lists.
• The technical contact's organisation is often, but not always, the back-end registry operator.
• Second-level endings like co.uk are read as their TLD, .uk.
• The limit is 100 extensions a run without an account and 500 signed in.

Check the addresses on those domains

Once you know who runs the extension, the address still has to exist. Upload your list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason, and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.

Look up your extensions now

Paste them into the TLD registry lookup.

Try a name in the free domain extension checker to compare extensions side by side.