$giden = "gidenmail@sitem.com";
$konu = "Konu";
$mesaj = "Bu Bir Mail";
$header .= "Reply-To: Mail Basligi<mail@sitem.com>\r\n"; 
$header .= "Return-Path: Mail Basligi <mail@sitem.com>\r\n"; 
$header .= "From: Mail Basligi <mail@sitem.com>\r\n"; 
$header .= "Content-Type: text/plain\r\n"; 
mail($giden, $konu, $mesaj, $header);