Issue with multiple checkboxes in a form - php

Question

I considered myself fairly adept at PHP and form processing before this. Now I've run into an issue and can't figure it out despite having going over my code time and time again. Naturally I've browsed StackOverflow and followed many examples as closely as I could, but nothing has fixed my issue, so it seems I'm missing something.
The form retrieves checked materials from the user as an array and puts them in an email body, or at least it should.
The HTML form with a checkbox array:
<div id="contact" class="form-container">
<fieldset>
<div id="message"></div>
<form method="post" action="get-quote.php" name="contactform" id="contactform">
<div class="form-group">
<input name="name" id="name" type="text" value="" placeholder="Name" class="form-control">
</div>
<div class="form-group">
<input name="email" id="email" type="text" value="" placeholder="Email" class="form-control">
</div>
<div class="form-group">
<input name="phone" id="phone" type="text" value="" placeholder="Phone" class="form-control">
</div>
<div class="form-group">
<label>Job Type / Material</label>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="sand">
Sand
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="select_fill">
Select Fill
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="common_fill">
Common Fill
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="top_soil">
Top Soil
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="stabilized_sand">
Stabilized Sand
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="crushed_concrete">
Crushed Concrete
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="milled_asphalt">
Milled Asphalt
</label>
</div>
<div class="checkbox">
<label>
<input type="checkbox" name="material[]" value="bull_rock">
Bull Rock
</label>
</div>
</div>
<div class="form-group">
<textarea name="comments" id="comments" class="form-control" rows="3" placeholder="Message"></textarea>
<div class="editContent">
<p class="small text-muted"><span class="guardsman">* All fields are required.</span> Once we receive your message we will respond as soon as possible.</p>
</div>
</div>
<div class="form-group">
<button class="btn btn-primary" type="submit" id="cf-submit" name="submit">Send</button>
</div>
</form>
</fieldset>
</div><!-- /.form-container -->
And the PHP:
<?php
if(!$_POST) exit;
// Email address verification, do not edit.
function isEmail($email) {
return(preg_match("/^[-_.[:alnum:]]+#((([[:alnum:]]|[[:alnum:]][[:alnum:]-]*[[:alnum:]])\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|me|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)$|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i",$email));
}
if (!defined("PHP_EOL")) define("PHP_EOL", "\r\n");
$name = $_POST['name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$comments = $_POST['comments'];
if(trim($name) == '') {
echo '<div class="error_message">Please enter your name.</div>';
exit();
} else if(trim($email) == '') {
echo '<div class="error_message">Please enter a valid email address.</div>';
exit();
} else if(trim($phone) == '') {
echo '<div class="error_message">Please enter a valid phone number.</div>';
exit();
} else if(!is_numeric($phone)) {
echo '<div class="error_message">Phone number can only contain digits.</div>';
exit();
} else if(!isEmail($email)) {
echo '<div class="error_message">You have entered an invalid e-mail address, try again.</div>';
exit();
}
if(trim($comments) == '') {
echo '<div class="error_message">Please enter your message.</div>';
exit();
}
if(get_magic_quotes_gpc()) {
$comments = stripslashes($comments);
}
$materials = isset($_POST['material']) ? implode(', ', $_POST['material']) : 'none';
// Configuration option.
// Enter the email address that you want to emails to be sent to.
// Example $address = "yourname#yourdomain.com";
$address = "myemail#gmail.com";
// Configuration option.
// i.e. The standard subject will appear as, "You've been contacted by John Doe."
// Example, $e_subject = '$name . ' has contacted you via Your Website.';
$e_subject = 'You\'ve been contacted by ' . $name . '.';
// Configuration option.
// You can change this if you feel that you need to.
// Developers, you may wish to add more fields to the form, in which case you must be sure to add them here.
$e_body = "You have been contacted by $name from your website, their message is as follows." . PHP_EOL . PHP_EOL;
$e_content = "\"$comments\"" . PHP_EOL . PHP_EOL;
$e_materials = "They specified the following materials: " . $materials . "." . PHP_EOL . PHP_EOL;
$e_reply = "You can contact $name by email, $email or by phone $phone";
$msg = wordwrap( $e_body . $e_content . $e_material . $e_reply, 70 );
$headers = "From: $email" . PHP_EOL;
$headers .= "Reply-To: $email" . PHP_EOL;
$headers .= "MIME-Version: 1.0" . PHP_EOL;
$headers .= "Content-type: text/plain; charset=utf-8" . PHP_EOL;
$headers .= "Content-Transfer-Encoding: quoted-printable" . PHP_EOL;
if(mail($address, $e_subject, $msg, $headers)) {
// Email has sent successfully, echo a success page.
echo "<fieldset>";
echo "<div id='success_page'>";
echo "<h2>Email Sent Successfully.</h2>";
echo "<p>Thank you <strong>$name</strong>, your message has been sent to us.</p>";
echo "</div>";
echo "</fieldset>";
} else {
echo 'ERROR!';
}
I didn't build the whole form or email script, I was just asked to get the checkboxes to work. And everything BUT the checkboxes work. Performing a var_dump on $_POST['material'] returns NULL regardless of whether or not boxes are checked.
Any help would be appreciated, as I've gone over this many times without seeing an issue with the code.