// plain

1. First, check the version of OpenSSL installed on your server. This can be done by running the command openssl version from the command line.
2. If the version is not up to date, update it.
3. Check the php.ini file to make sure the openssl extension is enabled.
4. Make sure the SMTP settings are configured correctly in PHPMailer.
5. Test the connection using the SMTP class in PHPMailer:

require 'PHPMailerAutoload.php';
$mail = new PHPMailer();
$mail->isSMTP();
$mail->Host = 'smtp.example.com';
$mail->Port = 587;
$mail->SMTPSecure = 'tls';
$mail->SMTPAuth = true;
$mail->Username = 'username';
$mail->Password = 'password';

if (!$mail->smtpConnect()) {
    echo 'Connection failed!';
    echo '<pre>' . print_r($mail->getError(), true) . '</pre>';
} else {
    echo 'Connection successful!';
}

6. If the connection fails, check the error message for more information.
7. If necessary, consult the PHPMailer documentation for more troubleshooting tips.

onelinerhub: How can I troubleshoot a PHPMailer OpenSSL error?