Sender Policy Framework

One reason to start with DNS was to be able to delegate authority over parts of the name space to others. Part of the tree can be separated from the rest and get its own keeper. This can be repeated. For instance, the keeper of the entire tree has delegated authority over "com." to someone else. This someone else has delegated authority over "example.com." to yet someone else.

Important to understand is this: the keeper of "example.com." does not have authority over domain "example.com." but over the entire zone "example.com.".