Mail function on IIS

[ukiEMAIL@gmail.com]

Hi
I've configured smtp and pop3 on server with IIS. I test if it is
working using outlook. I've sent successfully e-mail to myself and to
other accouts of my friends.
Unfortunatelly I'm stuck with configuring php that mail function will
send emails.
Steps that I've made to do so were:
- I've set smtp = my.smtp port = 25 and sendmail_from = my@mail.com
in my php.ini file.
- I wrote simple script
<?php
$to = "my@mail.co m";
$subject = "Hi!";
$body = "thi is content";
if (mail($to, $subject, $body)) {
echo("<p>Messag e successfully sent!</p>");
} else {
echo("<p>Messag e delivery failed...</p>");
}

?>

And as you probably know the script's output is Message delivery
failed...

Is there an extra module or thing that I have to do??
Do I have to enable some additional features??