Is it necessary to include the if($res) part in the PHP mail function for successful email sending?

The if($res) part in the PHP mail function is not necessary for successful email sending, but it can be useful for error handling and checking if the email was sent successfully. It allows you to take different actions based on the result of the mail function, such as displaying a success message or logging any errors that occurred during the sending process.

// Send email
$res = mail($to, $subject, $message, $headers);

// Check if the email was sent successfully
if($res) {
    echo "Email sent successfully";
} else {
    echo "Failed to send email";
}