艰巨的任务。。。

function wpse27756_restrict_register_email( $user_email ) {
    $errors = new WP_Error();

    if ( ! preg_match( "/gmail/i", $user_email ) {
        $errors->add( \'invalid_email\', __( \'<strong>ERROR</strong>: You are not allowed to use other mail accounts than Gmail.\' ) );
    }
    return $errors;
}

function wpse27756_add_register_email_filter( $user_email ) {
    add_filter( \'user_registration_email\', \'wpse27756_restrict_register_email\' );
}
add_action( \'init\', \'wpse27756_add_register_email_filter\' );

通过在主题函数中编写代码，可以轻松完成这一任务。php文件。代码如下：

    function is_valid_email_domain($login, $email, $errors ){
 $valid_email_domains = array("gmail.com","yahoo.com");// whitelist email domain lists
 $valid = false;
 foreach( $valid_email_domains as $d ){
 $d_length = strlen( $d );
 $current_email_domain = strtolower( substr( $email, -($d_length), $d_length));
 if( $current_email_domain == strtolower($d) ){
 $valid = true;
 break;
 }
 }
 // if invalid, return error message
 if( $valid === false ){
 $errors->add(\'domain_whitelist_error\',__( \'<strong>ERROR</strong>: you can only register using @gmail.com or @yahoo.com emails\' ));
 }
}
add_action(\'register_post\', \'is_valid_email_domain\',10,3 );