PHP Email is not sent but result is true

Question

I am using following code to send email from a windows server

$message = "Email From Sami";
$to = 'myid@gmail.com';
$subject = " test colr";
ini_set('display_errors',1);
$mail=mail($to, $subject,$message );
if($mail)
{
    echo "Thank you for using our mail form"; // I am getting this message
}
else
{
    echo "Mail sending failed."; 
}

But neither I am getting any error nor email is being received at target email (I have tried different target email addresses).

I have set smtp=localhost and port=25 in php.ini already. On the same server mail is being sent successfully from iis (Microsoft server). But getting no error or result from php mail