You should always test [man]mail/man:
$success = mail($to,$subject,$msg,$headers);
if ($success) {
$feedback_html = "<p>Your message was accepted for delivery.</p>";
} else {
$feedback_html = "<p>There was a problem with your message. Please try again or contact our support staff.</p>";
}
That being said, there are plenty of other things that could go wrong with sending mail. See if you can send a simple plain-text test message with your code before trying the heavyweight HTML version of a sales pitch --- there's so much spam filtering out there (and it's badly needed).
Try sending to a variety of different addresses. That means you need friends or a lot of email accounts with different providers.
Check your webserver logs. There could be something there to help diagnose the issue.
Finally, someone runs the real server. If it's you, check the mail server logs. If not, that's what "support" is for. Open a ticket and push them (gently at first) to get to the bottom of it.
HTH,