php 发送邮件乱码

 php发送邮箱乱码   ：（缺少加红部分）   
                $mail = new PHPMailer();
                $mail->IsSMTP();
                $mail->SMTPAuth = true;
                $mail->Host = $smtp;
                $mail->Username = $youremail;
                $mail->Password = $password; //必填， 以上邮箱对应的密码
                $mail->From = $youremail;
                $mail->FromName = $site_name; //发件人称呼
                $mail->AddAddress($ymail,$yname);
                $mail->CharSet = "utf-8";