How can PHP developers prevent common SMTP server errors like "Bad sequence of commands" when sending emails through PHPMailer?

To prevent common SMTP server errors like "Bad sequence of commands" when sending emails through PHPMailer, PHP developers can ensure that the SMTP connection is properly initialized before attempting to send the email. This can be done by setting the SMTPDebug property to 2 in PHPMailer, which enables debugging output to track the SMTP communication and identify any issues. 

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

// Load Composer's autoloader
require 'vendor/autoload.php';

// Instantiation and passing `true` enables exceptions
$mail = new PHPMailer(true);

try {
    //Server settings
    $mail->SMTPDebug = SMTP::DEBUG_SERVER; // Enable verbose debug output
    $mail->isSMTP();
    $mail->Host = 'smtp.example.com';
    $mail->SMTPAuth = true;
    $mail->Username = 'your@example.com';
    $mail->Password = 'yourpassword';
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;
    $mail->Port = 587;

    //Recipients
    $mail->setFrom('from@example.com', 'Mailer');
    $mail->addAddress('joe@example.net', 'Joe User');

    // Content
    $mail->isHTML(true);
    $mail->Subject = 'Here is the subject';
    $mail->Body    = 'This is the HTML message body <b>in bold!</b>';

    $mail->send();
    echo 'Message has been sent';
} catch (Exception $e) {
    echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}

Keywords

PHP SMTP server PHPMailer error handling email sending

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