PHP contact form

     <form name="contactform" method="post" action="send_form_email.php"> <!--id="ajax-contact" method="post" action="mailer.php"> current option from http://www.freecontactform.com/email_form.php-->
      <div class="form-group row field">
        <label for="name" class="col-sm-2 col-form-label">Name:</label>
        <div class="col-sm-6 col-lg-4">
          <input type="text" class="form-control" id="name" placeholder="Your Full Name" name="name" required>
        </div>
      </div>
       <div class="form-group row field">
        <label for="email" class="col-sm-2 col-form-label">Email:</label>
        <div class="col-sm-6 col-lg-4">
          <input type="email" class="form-control" id="email" placeholder="youremail@example.com" name="email" required>
        </div>
      </div>
       <div class="form-group row field">
        <label for="message" class="col-sm-2 col-form-label">Message:</label>
        <div class="col-md-8">
          <textarea class="form-control" id="message" rows="6" placeholder="Type your message" name="message" required></textarea>
        </div>
      </div>
         <div class="field">
            <input type="submit" class="btn btn-primary d-block m-x-auto" value="Send Message">
         </div>
    </form>

  </div>

// EDIT THE 2 LINES BELOW AS REQUIRED

$email_to = "email@email.com";

$email_subject = "New message";





function died($error) {

    // your error code can go here

    echo "We are very sorry, but there were error(s) found with the form you submitted. ";

    echo "These errors appear below.<br /><br />";

    echo $error."<br /><br />";

    echo "Please go back and fix these errors.<br /><br />";

    die();

}



// validation expected data exists

if(!isset($_POST['name']) ||

    !isset($_POST['email']) ||

    !isset($_POST['message'])) {

    died('We are sorry, but there appears to be a problem with the form you submitted.');       

}



$name = $_POST['name']; // required

$email_from = $_POST['email']; // required

$message = $_POST['message']; // required



$error_message = "";

$email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';

$error_message .= 'The Email Address you entered does not appear to be valid.<br />';

$string_exp = "/^[A-Za-z .'-]+$/";

$error_message .= 'The Name you entered does not appear to be valid.<br />';

$error_message .= 'The Comments you entered do not appear to be valid.<br />';

died($error_message);

$email_message = "Form details below.\n\n";



function clean_string($string) {

  $bad = array("content-type","bcc:","to:","cc:","href");

  return str_replace($bad,"",$string);

}



$email_message .= "Name: ".clean_string($name)."\n";

$email_message .= "Email: ".clean_string($email_from)."\n";

$email_message .= "Comments: ".clean_string($message)."\n";