Sending mail with PHPMailer (SMTP)

Question

I am trying to send mail with PHPMailer (SMTP). If I send from localhost I get the error warning:

2017-11-11 15:14:39 SERVER -> CLIENT: 220 2.0.0 Ready to start TLS 2017-11-11 15:14:40 Connection failed. Error #2: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages:error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed [C:\xampp\htdocs\NEU\phpmailer\vendor\phpmailer\phpmailer\src\SMTP.php line 404] SMTP Error: Could not connect to SMTP host. 2017-11-11 15:14:40 CLIENT -> SERVER: QUIT

I've read about changing ssl options like this:

$mail->SMTPOptions = array(
                        'ssl' => array(
                            'verify_peer' => false,
                            'verify_peer_name' => false,
                            'allow_self_signed' => true
                        )
                    );

This is working for me, but I guess there should be another option to fix the problem, since this doesn't fix it on the actual server. On the server the browser just keeps loading for a while until I get an 504 error or even the message:

Failed to load resource: net::ERR_INCOMPLETE_CHUNKED_ENCODING

Now I don't really now how to fix the problem, since I'm really new into this. I've also read about some Problems with ssl certification but didn't come to any conclution...

My Requestcode:

<?php

    // Import PHPMailer classes into the global namespace
    use PHPMailer\PHPMailer\PHPMailer;

    //Load composer's autoloader
    require 'phpmailer/vendor/autoload.php';

    //Empfänger E-Mail
    $recipient = 'recipient@web.de';

    //Formularfelder
    $vname = trim($_POST['vname']);
    $name = trim($_POST['name']);
    $email = trim($_POST['email']);
    $message = trim($_POST['message']);

    if($name != null && $email != null && $message != null) {
        if (!filter_var($email, FILTER_VALIDATE_EMAIL) === false) {

                    $mail = new PHPMailer(true);                                    // Passing `true` enables exceptions

                    //Server settings
                    $mail->isSMTP();                                                // Set mailer to use SMTP
                    $mail->SMTPDebug = 2;
                    $mail->Host = 'smtp.gmail.com';                         // Specify main and backup SMTP servers
                    $mail->SMTPAuth = true;                                     // Enable SMTP authentication
                    $mail->Username = 'username@gmail.com';     // SMTP username
                    $mail->Password = 'passowrd';                       // SMTP password
                    $mail->SMTPSecure = 'tls';                                  // Enable TLS encryption
                    $mail->Port = 587;                                      // TCP port to connect to

                    /*$mail->SMTPOptions = array(
                        'ssl' => array(
                            'verify_peer' => false,
                            'verify_peer_name' => false,
                            'allow_self_signed' => true
                        )
                    );  */

                    //Recipients
                    $mail->setFrom("$recipient", '**');
                    $mail->addAddress("$recipient", '**');     // Add a recipient 
                    $mail->addReplyTo($email, $name);

                    $body = "<p><strong>Name: </strong>$vname $name <br> <strong>Nachricht: </strong>$message</p>";

                    //Content
                    $mail->isHTML(true);                                     // Set email format to HTML
                    $mail->Subject = 'Kontaktformular';
                    $mail->Body    = $body;
                    $mail->AltBody = strip_tags($body);

                    if(!$mail->send()){
                        $signal = 'bad';
                        $msg = 'Mailer Error: ' . $mail->ErrorInfo;
                    } else {
                        $signal = 'ok';
                        $msg = 'Nachricht versendet, vielen Dank!';
                    }

        } else {
            $signal = 'bad';
            $msg = 'Ungültige E-Mail-Adresse, bitte versuchen Sie es erneut.';
        }
    } else {
        $signal = 'bad';
        $msg = 'Bitte füllen Sie alle erforderlichen Felder aus.';
    }

    $data = array(
        'signal' => $signal,
        'msg' =>  $msg
    );

    echo json_encode($data);

?>

I hope that you can help me, if you need some more information just ask for them. I'm sorry that my english isn't the best. Best regards