Gmail users among authors
Search among the sites authors for Gmail users and return their email addresses.
// WP_User_Query arguments $args = array ( 'search' => '@gmail.com', 'search_columns' => array( 'user_email' ), 'who' => 'authors', 'fields' => array( 'user_email' ), ); // The User Query $user_query = new WP_User_Query( $args );