I got a strange behavior from the mail function in php here is the code :

$header = "From: aa@aa.com\n";
 $header .= "Reply-To: bb@bb.com\n";
 $header .= "Content-Type: multipart/alternative; boundary=$alt_boundary\n"; 
 $header .= "Mime-Version: 1.0\n";
 $header .= "X-Mailer: PHP/".phpversion()."\n";
 $header .= "Content-Type: text/plain;charset=utf-8\n";

 $send = mail($to,$subject,$message,$headers);

user123@s12panelboxmanage.com: ama aldığınız e-posta gibi sunucusunun ana yönetici bir gelen adresi var

neden?