WHOIS is a protocol used for querying databases that store registered user information on resources such as domain names and IP addresses.
Using a WHOIS search provides information on domain names. Depending on how the search is done, it can also include domain ownership, expiration date, and the nameservers assigned to the domain.
Websites that enable you to conduct a WHOIS search include:
Certified senders need to have WHOIS records that are set up correctly, have accurate contact information, and do not hide domains behind privacy services.