Start of Authority (SOA) is a set of data that provides critical resources for the Domain Name System that helps to validate domains on the Internet. The Domain Name System, maintained by Internet Corporation for Assigned Names and Numbers (ICANN) and a community of registrars, sorts out ownership and control rights for specific domains. The SOA element contains information about the host for a particular domain, as well as a basket of information about how long it takes a host server to refresh the domain, to respond to messages or to retry failed operations.
Experts point out that technically, the SOA record refers to a DNS zone instead of a domain. The zone is simply the portion of a domain that is controlled by a particular server. One server can control many domains, but the SOA helps to establish the primary server for the individual zone, thus helping to point toward the correct working operator for that zone. Without this protocol, it would be much harder to collect and use the information that resides in the SOA.