$to = 'recipient@example.com'; $subject = 'Test email'; $message = 'This is a test message'; $headers = "From: sender@example.com\r\n"; $headers .= "Content-type: text/plain\r\n"; mail($to, $subject, $message, $headers);In this example, we are specifying the recipient's email address, the email subject, and the email message. We also define the email headers, such as the sender's email address and the content type. It's important to note that the `mail()` function relies on the server configuration to send the email. If the server doesn't have the necessary configuration or if the email is flagged as spam, the email may not be delivered. Additionally, there are several third-party PHP libraries that provide more advanced email sending features, such as HTML email templates, SMTP authentication, and email tracking. Examples of such libraries include PHPMailer, SwiftMailer, and Zend Mail.