$message = "Hello, this is a message."; $sender = "user@example.com"; $recipient = "you@example.com"; // send message mail($recipient, "Message from $sender", $message); // reply to message $reply = "Thanks for your message. I will get back to you soon."; mail($sender, "Message response", $reply);In this example, we first send a message from the sender `$sender` to the recipient `$recipient`. Then, we use the `mail` function again to reply to the message from the sender to the recipient. The PHP `mail` function is a built-in function in PHP that sends an email. It is part of the PHP mail package library. Overall, PHP Message reply is a useful feature for communication applications that require sending and receiving messages. It is easy to implement using the built-in `mail` function in PHP.