Send email with PHP over SMTP (PHPMailer)

composer require phpmailer/phpmailer

<?php
require 'vendor/autoload.php';

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$mail = new PHPMailer(true);
try {
    $mail->isSMTP();
    $mail->Host       = getenv('SMTP_HOST') ?: 'smtp.queensmtp.com';
    $mail->Port       = 587;
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;   // use ENCRYPTION_SMTPS + port 465 for implicit TLS
    $mail->SMTPAuth   = true;
    $mail->Username   = getenv('SMTP_USER');
    $mail->Password   = getenv('SMTP_PASS');

    $mail->setFrom('hello@yourdomain.com', 'Your App');   // must be a verified sending domain
    $mail->addAddress('customer@example.com', 'Customer');
    $mail->addReplyTo('support@yourdomain.com');

    $mail->isHTML(true);
    $mail->Subject = 'Your receipt';
    $mail->Body    = '<h1>Thanks for your order</h1><p>Order #1042 is confirmed.</p>';
    $mail->AltBody = "Thanks for your order\nOrder #1042 is confirmed.";
    // $mail->addAttachment('/path/invoice-1042.pdf');

    $mail->send();
    echo "sent\n";
} catch (Exception $e) {
    error_log('SMTP error: ' . $mail->ErrorInfo);
}