$headers[] = "Content-type: text/html; charset=UTF-8";
// ...
// ...
$headers[] = "Content-Transfer-Encoding: base64";
$subject = '=?utf-8?B?'.base64_encode($subject).'?=';
$message = chunk_split(base64_encode($message), 76, "\n");
mail($mail_to, $subject, $message, implode("\r\n", $headers));$mail->From = "login@your-domain.com";
echo '<meta property="og:title" content="', single_cat_title(), '"/>';