解決PHP寄信時主旨及內容顯示亂碼

當PHP寄信時，顯示亂碼時，該如何處理?

$email = "test@email.com.tw" //收件人
$header = "From:Jacky<jacky@email.com.tw>\r\nReply-to:jacky@email.com.tw\r\nContent-Type:text/html; Charset:big5"; //寄件人
$subject = "我的主旨"; //主旨
$content = "我的內容"; //內容



$header = mb_convert_encoding($header,"big5","utf8"); //將寄件人由utf8轉為big5編碼
$subject = mb_convert_encoding($subject,"big5","utf8");//將主旨由utf8轉為big5編碼
$content = mb_convert_encoding($content,"big5","utf8");//將內容由utf8轉為big5編碼
mail( $email, $subject, $content, $header ); //將信件寄出