ส่งเมล์ไม่ได้ครับ ผู้รู้ช่วยหน่อยครับ - Warning: mail(): SMTP server response:555 syntax error(#5.5.4) in

<?php 
$subject = "ติดต่อโรงเรียนนักเดินเรือ";
$header = $_POST['u_mail'];
$message = "จาก : " . $_POST['u_mail'] . "\r\n";
$message .= "ขื่อผู้ส่ง : " . $_POST['u_name'] . "\r\n";
$message .= "เบอร์โทรศัพท์ผู้ส่ง : " . $_POST['u_tel'] . "\r\n"; 
$message .= "ที่อยู่ผู้ส่ง : " . $_POST['u_address'] . "\r\n\n";
$message .= $_POST['u_text'] . "\n";

if($_POST['u_chk'] == 1 )
{
	$to  = "[email protected], $header" ;
}
else
{
	$to = "[email protected]";
}

ini_set("SMTP","203.150.225.191");
ini_set("sendmail_from", "$header" ); 
ini_set(smtp_port,25);

$mail_ok =  mail($to , $subject , $message);
if($mail_ok)
{
?>
		<script language="JavaScript" type="text/JavaScript">
			 alert("Sending mail sucessfull");
		</script>
		<?php
			echo "<meta http-equiv='refresh' content='0; URL=contact.php'>";
}
else
{
?>
		<script language="JavaScript" type="text/JavaScript">
			 alert("Sending mail fail");
		</script>
		<?php
			echo "<meta http-equiv='refresh' content='0; URL=contact.php'>";
}
?>