<?php
// Import PHPMailer classes into the global namespace
// These must be at the top of your script, not inside a function
use PHPMailerPHPMailerPHPMailer;
use PHPMailerPHPMailerException;


// 'PHPMailer' here actually is the original folder 'PHPMailer-master'
// from unpacking the downloaded file PHPMailer-master.zip
require 'vendor/PHPMailer/src/Exception.php';
require 'vendor/PHPMailer/src/PHPMailer.php';
require 'vendor/PHPMailer/src/SMTP.php';

echo (extension_loaded('openssl')?'SSL loaded':'SSL not loaded')."n";

$mail = new PHPMailer(true);         // Passing `true` enables exceptions
try {
    //Server settings
    $mail->SMTPDebug = 2;            // Enable verbose debug output

    $mail->isSMTP();
    $mail->Host = 'smtp.kabelmail.de';          //smtp1.example.com;smtp2.example.com';  // Specify main and backup SMTP servers
    $mail->SMTPAuth = true;                 // Enable SMTP authentication
    $mail->Username = 'myname@kabelmail.de';     // SMTP username
    $mail->Password = 'mypassword';              // SMTP password
    $mail->SMTPSecure = 'tls'; // Enable TLS encryption, `ssl` also accepted
    $mail->Port = 465;                           // TCP port to connect to

    //Recipients
    $mail->setFrom('from@example.com', 'Mailer');
    $mail->addAddress('myname@kabelmail.de', 'myname');  // Add a recipient
    // $mail->addAddress('ellen@example.com');           // Name is optional
    $mail->addReplyTo('myname@web.de', 'Antwort');
    //$mail->addCC('cc@example.com');
    //$mail->addBCC('bcc@example.com');

    //Attachments
    //$mail->addAttachment('/var/tmp/file.tar.gz');     // Add attachments
    //$mail->addAttachment('/tmp/image.jpg', 'new.jpg');    // Optional name

    //Content
    $mail->isHTML(true);                        // Set email format to HTML
    $mail->Subject = 'Here is the subject:localhost';
    $mail->Body    = 'This is the HTML message body <b>in bold!</b>';
    $mail->AltBody = ' body in plain text for non-HTML mail lients';

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

[mail function]
SMTP=smtp.kabelmail.de
smtp_port=465
sendmail_from = to@kabelmail.de
sendmail_path ="C:xamppsendmailsendmail.exe"
;(I also tried sendmail_path = ""C:xamppsendmailsendmail.exe" -t" but without success.)
mail.log="C:xamppphplogsphp_mail.log"

[sendmail]
smtp_server=smtp.kabelmail.de
smtp_port=465
smtp_ssl=auto
error_logfile=error.log
debug_logfile=debug.log
auth_username=myname@kabelmail.de
auth_password=mypassword

SSL loaded 2018-01-11 12:06:10 SERVER -> CLIENT: 421 4.3.2 Too many open connections.
2018-01-11 12:06:10 CLIENT -> SERVER: EHLO localhost
2018-01-11 12:06:10 SERVER -> CLIENT:
2018-01-11 12:06:10 SMTP ERROR: EHLO command failed:
2018-01-11 12:06:10 SMTP NOTICE: EOF caught while checking if connected
SMTP Error: Could not connect to SMTP host.
SMTP Error: Could not connect to SMTP host.
Message could not be sent.Mailer Error: SMTP Error: Could not connect to SMTP host.

[11-Jan-2018 13:09:32 Europe/Berlin] mail() on [C:xampphtdocstovendorPHPMailersrcPHPMailer.php:768]: To: "name" <myname@kabelmail.de> -- Headers: Date: Thu, 11 Jan 2018 13:09:32 +0100  From: Mailer <from@example.com>  Reply-To: Antwort <myname@web.de>  Message-ID: <VuAQ3BR022MQyNd3hKCoguqr50Ry9TPG4vIRL2ZmFg@localhost>  X-Mailer: PHPMailer 6.0.3 (https://github.com/PHPMailer/PHPMailer)  MIME-Version: 1.0  Content-Type: multipart/alternative;     boundary="b1_VuAQ3BR022MQyNd3hKCoguqr50Ry9TPG4vIRL2ZmFg"  Content-Transfer-Encoding: 8bit