Form validation evaluation to avoid exploits

Question

Please advise if the form validation script below is secure enough to avoid most types (all types?) of contact form exploits? I ahve found this script online, added some extra php finctions in hope to make it safer, but not complitely sure if it is good for the purpose.

if ($_SERVER["REQUEST_METHOD"] == "POST" && !empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
 // Get the form fields and remove whitespace.
 $name = strip_tags(trim($_POST["name"]));
 $name = str_replace(array("\r","\n"),array(" "," "),$name);
 $email = filter_var(trim($_POST["email"]), FILTER_SANITIZE_EMAIL);
 $message = strip_tags(trim($_POST["message"]));
 // Check that data was sent to the mailer.
 if ( empty($name) OR empty($message) OR !filter_var($email, FILTER_VALIDATE_EMAIL)) {
 // Set a 400 (bad request) response code and exit.
 //http_response_code(400);
 echo "Oops! There was a problem with your submission. Please complete the form and try again.";
 exit;
 }
 // Set the recipient email address.
 // FIXME: Update this to your desired email address.
 $recipient = "email_here";
 // Set the email subject.
 $subject = "New contact from $name";
 // Build the email content.
 $email_content = "Name: $name\n";
 $email_content .= "Email: $email\n\n";
 $email_content .= "Message:\n$message\n";
 // Build the email headers.
 $email_headers = "MIME-Version: 1.0\r\n";
 $email_headers .= "Content-type: text/html; charset=utf-8\r\n"; 
 $email_headers .= "From: $name <$email>\r\n";
 $email_headers .= "Reply-To: $email\r\n";
 $email_headers .= "Return-Path: $email\r\n";
 $email_headers .= "Organization: Bilingual Counselling\r\n"; 
 // Send the email.
 if (mail($recipient, $subject, $email_content, $email_headers)) {
 // Set a 200 (okay) response code.
 //http_response_code(200);
 echo "Thank You! Your message has been sent.";
 } else {
 // Set a 500 (internal server error) response code.
 //http_response_code(500);
 echo "Oops! Something went wrong and we couldn't send your message.";
 }
}

Answer 1

I think it looks ok - though someone might want to add on if they notice any issues I may have missed. However, a bit of cleanup goes a long way:

# Set a 500 (internal server error) response code.
function outputResponse($override = "", $code = 500){
 # http_response_code($code);
 echo $override ?: "Oops! Something went wrong and we couldn't send your message.";
 exit;
}
# Exit early while doing negative checks
if(empty($_SERVER['HTTP_X_REQUESTED_WITH'] || 
 strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest' || 
 $_SERVER["REQUEST_METHOD"] != "POST"){
 outputResponse();
}
# Get the form fields and remove whitespace.
$name = strip_tags(trim($_POST["name"]));
$name = str_replace(array("\r","\n"),array(" "," "),$name);
$email = filter_var(trim($_POST["email"]), FILTER_SANITIZE_EMAIL);
$message = strip_tags(trim($_POST["message"]));
# Check that data was sent to the mailer.
if ( empty($name) OR empty($message) OR !filter_var($email, FILTER_VALIDATE_EMAIL)) {
 # Set a 400 (bad request) response code and exit.
 outputResponse("Oops! There was a problem with your submission. Please complete the form and try again.", 400);
}
# Set the recipient email address.
$recipient = "email_here";
# Set the email subject.
$subject = "New contact from $name";
# Build the email content.
$email_content = "Name: $name\n";
$email_content .= "Email: $email\n\n";
$email_content .= "Message:\n$message\n";
# Build the email headers.
$email_headers = "MIME-Version: 1.0\r\n";
$email_headers .= "Content-type: text/html; charset=utf-8\r\n"; 
$email_headers .= "From: $name <$email>\r\n";
$email_headers .= "Reply-To: $email\r\n";
$email_headers .= "Return-Path: $email\r\n";
$email_headers .= "Organization: Bilingual Counselling\r\n"; 
# Send the email.
if (mail($recipient, $subject, $email_content, $email_headers)) {
 # Set a 200 (okay) response code.
 outputResponse("Thank you! Your message has beent sent.", 200)
} else {
 outputResponse();
}