Why isn't my php form sending any e-mail?

[Bleh22]

echo "<form method='post' action='testform.php'>
Username: <input type='text' name='username' size='20' />
<br /><br />
First Name: <input type='text' name='firstname' size='20' />
Last Name: <input type='text' name='lastname' size='20' />
<br /><br />
Birthday:
Day
<select name='day'>
<option value='01'>01</option>
<option value='02'>02</option>
</select>
Month
<select name='month'>
<option value='jan'>Jan</option>
<option value='feb'>Feb</option>
</select>
Year
<select name='year'>
<option value='2011'>2011</option>
<option value='2010'>2010</option>
<option value='2009'>2009</option>
</select>
<br /><br />
Gender:
<input type='radio' name='sex' value='Female' checked='checked' /> Female
<input type='radio' name='sex' value='Male' /> Male
<br /><br />
E-mail:<br />
<input type='text' name='email' size='40' />
<br /><br />
Question title:
<br />
<input type='text' name='subject' size='100' />
Question:<br />
<textarea name='question' rows='15' cols='40'>
</textarea><br />
<input type='submit' value='Send' />
<input type='reset' value='Reset' />
</form>";

I am not getting any errors but the form isn't sending an e-mail.

Thanks.
if (isset($_REQUEST['email']))
//if "email" is filled out, send email
{
//send email
$email = $_REQUEST['email'] ;
$subject = $_REQUEST['subject'] ;
$uname = $_REQUEST['username'] ;
$fname = $_REQUEST['firstname'] ;
$lname = $_REQUEST['lastname'] ;
$day = $_REQUEST['day'] ;
$month = $_REQUEST['month'] ;
$year = $_REQUEST['year'] ;
$sex = $_REQUEST['sex'];
$message = $_REQUEST['question'] ;
mail( "[email protected]", "Subject: $subject", "Username: $uname : Firstname: $fname : Lastname: $lname :
Birthday: $day:$month:$year : Gender: $sex", $message, "From: $email" );
echo "Thank you for using our mail form";
}