How can the use of external libraries or classes improve the reliability of email sending functions in PHP?

When sending emails in PHP, using external libraries or classes can improve reliability by providing more robust error handling, better support for various email protocols, and additional features such as email templating. These libraries often have been thoroughly tested and maintained by the community, reducing the likelihood of bugs or issues in the email sending functionality.

// Using PHPMailer library for reliable email sending
require 'vendor/autoload.php';

// Create a new PHPMailer instance
$mail = new PHPMailer\PHPMailer\PHPMailer();

// Set up the email parameters
$mail->isSMTP();
$mail->Host = 'smtp.example.com';
$mail->SMTPAuth = true;
$mail->Username = 'your@example.com';
$mail->Password = 'yourpassword';
$mail->SMTPSecure = 'tls';
$mail->Port = 587;

$mail->setFrom('from@example.com', 'Your Name');
$mail->addAddress('recipient@example.com', 'Recipient Name');
$mail->Subject = 'Test Email';
$mail->Body = 'This is a test email.';

// Send the email
if(!$mail->send()) {
    echo 'Message could not be sent.';
    echo 'Mailer Error: ' . $mail->ErrorInfo;
} else {
    echo 'Message has been sent';
}