What are the potential security concerns when including username, password, and encryption settings in the PHP mail configuration for external email services like GMX or Web.de?

Potential security concerns arise when including sensitive information like usernames, passwords, and encryption settings directly in the PHP mail configuration for external email services. This can lead to unauthorized access to the email account if the PHP file is compromised. To mitigate this risk, it is recommended to store these sensitive details in a separate configuration file outside of the web root directory and include them securely in the PHP script using environment variables or a secure configuration file.

// Load sensitive email configuration from a separate file
$config = include('/path/to/email_config.php');

// Use the configuration settings securely in the PHP mail function
$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host = $config['host'];
$mail->SMTPAuth = true;
$mail->Username = $config['username'];
$mail->Password = $config['password'];
$mail->SMTPSecure = $config['encryption'];
$mail->Port = $config['port'];