Basic PHP-based mail script for portfolio contact forms

mail.php

<?php
########################################################
### CONFIG ###
########################################################
const YOUR_EMAIL = 'YOUREMAIL@DOMAIN.COM';

//define a math problem as a field in your form to prevent spam;
//or use a word problem with a string as the answer, but be careful since the case and spelling of the user's answer will need to be exact
const ANSWER = 5;
########################################################
########################################################



//ensure that they submitted all the fields and answered the question correctly
if( !isset($_REQUEST['name'], $_REQUEST['email'], $_REQUEST['message'], $_REQUEST['answer']) || ANSWER != $_REQUEST['answer'] ){
	http_response_code(400); //client error
	die();
}

//capture and sanitize their answers
$name = filter_var($_REQUEST['name'], FILTER_SANITIZE_STRING);
$email = filter_var($_REQUEST['email'], FILTER_SANITIZE_EMAIL);
$message = filter_var($_REQUEST['message'], FILTER_SANITIZE_STRING);

//add their name+email at the end of their message
$message .= '<br><br><b>From: <a href="mailto:'.$email.'">'.$name.' &lt;'.$email.'&gt;</a></b>';

//configure the message
$subject = 'Message from Portfolio Contact Form';
$headers = array(
    'From: '.YOUR_EMAIL,
    'Content-Type:text/html;charset=UTF-8',
    'Reply-To: '.$name.' <'.$email.'>'
);
$headers = implode("\r\n", $headers); //MUST be double quotes

//send the mail
$mailSuccess = mail( YOUR_EMAIL, $subject, $message, $headers );
//NOTE: just because this function succeeds doesn't mean that the message successfully sent
//reasons for not receiving email: their/your email isn't legit; the mailserver is incorrectly configured; server-level spam detection

//return the request as appropriate
if( $mailSuccess ){
	http_response_code(200); //success
} else {
	http_response_code(500); //server error
}
die();

Some notes:

Required fields on your front-end <form>

• a text input name="name" (just asking for their name here)
• an email input name="email"
• a textarea name="message"
• any other field name="answer" (this can be anything: a math problem, a question, a hidden field set by a visual question with Javascript, etc. It must match up with the ANSWER constant in the PHP.)

The JavaScript

This PHP script is set to simply return the appropriate HTTP status codes, so it's perfect for AJAX requests. Change the alert()s to whatever is appropriate for your site: displaying a message, changing the interface, etc. Here is an example using jQuery.

$.post('mail.php', $( "#YOURFORMIDHERE" ).serialize()).done(function(data){
    alert('emailed successfully');
}).fail(function(){
    alert('error sending email');
});