<?php

    require_once("mailer/class.phpmailer.php");
    require_once("mailer/class.smtp.php");

    $mail = new PHPMailer();
    $mail->IsSMTP(); // telling the class to use SMTP

    $mail->SMTPSecure     = false;
    $mail->Host          = "mail.xxx.cz";
    $mail->SMTPAuth      = true;
    $mail->SMTPKeepAlive = true;
    $mail->Port          = 587;
    $mail->Username      = "michal@mail.xxx.cz";
    $mail->Password      = "TEST";
    $mail->SMTPDebug      = 3;

    $mail->FromName      = "Michal";
    $mail->From          = "michal@mail.xxx.cz";
    $mail->Subject       = "Newsletter";

    $mail->AltBody    = "To view the message, please use an HTML compatible email viewer!";
    $mail->MsgHTML("testing");
    $mail->AddAddress("filfareu@gmail.com");

    if(!$mail->Send()) {
        echo $mail->ErrorInfo;
        exit;
    }
    echo "Message has been sent";

?>

2016-01-08 12:03:35 Connection: opening to mail.xxx.cz:587, timeout=300, options=array (
                                      )
2016-01-08 12:03:35 Connection: opened
2016-01-08 12:03:35 SERVER -> CLIENT: 220 vm1xxxx ESMTP Postfix (Ubuntu)
2016-01-08 12:03:35 CLIENT -> SERVER: EHLO blog.xxx.cz
2016-01-08 12:03:35 SERVER -> CLIENT: 250-vm1xxxx
                                      250-PIPELINING
                                      250-SIZE 10240000
                                      250-VRFY
                                      250-ETRN
                                      250-ENHANCEDSTATUSCODES
                                      250-8BITMIME
                                      250 DSN
2016-01-08 12:03:35 SMTP Error: Could not authenticate.
2016-01-08 12:03:35 CLIENT -> SERVER: QUIT
2016-01-08 12:03:35 SERVER -> CLIENT: 221 2.0.0 Bye
2016-01-08 12:03:35 Connection: closed
2016-01-08 12:03:35 SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting