Simple script to test PHP mail is working

testmail.php

<?php
$sender = 'from@example.com';
$recipient = 'to@example.com';

$subject = "PHP Mail Test Message";
$message = "PHP Mail Test Message";
$headers = [
    'From: ' . $sender,
    'Sender: ' . $sender,
];

if (mail($recipient, $subject, $message, implode("\n", $headers))) {
    echo "Message sent!";
} else {
    echo "Error: ".error_get_last()['message'];
}