How can the code be modified to include the submission date in the email message sent?

To include the submission date in the email message sent, you can modify the PHP code to retrieve the current date and time and include it in the email message body. This can be achieved by using the `date()` function in PHP to format the current date and time in the desired format.

<?php
// Get the current date and time
$submission_date = date("Y-m-d H:i:s");

// Email message with submission date included
$message = "Thank you for your submission. Your form was received on: $submission_date";

// Send email with submission date included
mail($to, $subject, $message, $headers);
?>