E-Mail problems

I am getting an error when I try to send e-mail through php…Warning: mail(): SMTP server response: 550 5.7.1 Unable to relay for [email][email protected][/email] in c:inetpubwwwrootaaa.php on line 15

my code is

[code=php]<?php
$to = “[email protected]”;
$from = “USER”;
$subject = “Test”;
$body = “This is just a test message”;
print “Thanks for contacting us.<br><br>”;
mail ($to,$subject,$body,$from);
?>[/code]

I’ve seen a lot of email codes and to me this looks like the same but it doesn’t work, anybody know what I’m doing from?

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