my $public_key = Mail::DKIM::PublicKey->fetch(
                      Protocol => "dns",
                      Selector => "brisbane",
                      Domain => "example.com",
                    );

If the public key is found, a Mail::DKIM::PublicKey object is returned, representing the information found in DNS. If the public key does not exist in DNS, then undef is returned. If a DNS error occurs while fetching the key, then this method will die. If the public key was found, but is not valid (e.g. it is "revoked"), then this method will die.

  my $g = $public_key->granularity;

  $public_key->granularity("*");

Granularity of the key. The value must match the Local-part of the effective "i=" tag of the DKIM-Signature header field. The granularity is a literal value, or a pattern with a single '*' wildcard character that matches zero or more characters.

If no granularity is defined, then the default value, '*', will be returned.