require_once($CFG->dirroot.'/lib/phpmailer/moodle_phpmailer.php');

		$mail = new PHPMailer();
        $mail->isSMTP();                                      // Set mailer to use SMTP
        $mail->Host = $CFG->smtphosts;                       // Specify main and backup server
        $mail->Port = 587;
        $mail->SMTPAuth = true;
        $mail->Username = $CFG->smtpuser;                 // SMTP username
        $mail->Password = $CFG->smtppass;
        $mail->SetFrom($CFG->smtpuser); // Enable SMTP authentication
        $mail->addAddress($user->email);  // Add a recipient
        $mail->isHTML(true);
        $mail->setLanguage('pl', $CFG->dirroot.'/lib/phpmailer/language/phpmailer.lang-pl.php');
        $mail->CharSet = 'UTF-8';

        $startdate          = strftime('%Y%m%d', $enrol->timestart - 60*60);
        $startTime          = strftime('%H%M', $enrol->timestart - 60*60);
        $enddate            = strftime('%Y%m%d', $enrol->timeend - 60*60);
        $endTime            = strftime('%H%M', $enrol->timeend - 60*60);

        $a = new stdClass();
        $a->user = fullname($user);
        $a->fullname = $course->fullname;
        $a->startdate = strftime('%d.%m.%Y %H:%M', $enrol->timestart - 60*60);
        $a->enddate = strftime('%d.%m.%Y %H:%M', $enrol->timeend - 60*60);

        $subject = get_string('email_header', 'local_enrolmail', $a);
        $body = get_string('email_body', 'local_enrolmail', $a);

        $mail->addCustomHeader('Content-Type:text/calendar');
        $mail->addCustomHeader('Content-Disposition: inline');
        $mail->addCustomHeader('charset=utf-8');

        // outlook calendar attachment
        $text = "BEGIN:VCALENDAR\r\n
                VERSION:2.0\r\n
                PRODID:-//Deathstar-mailer//theforce/NONSGML v1.0//EN\r\n
                METHOD:REQUEST\r\n
                BEGIN:VEVENT\r\n
                UID:" . md5(uniqid(mt_rand(), true)) . "example.com\r\n
                DTSTAMP:" . gmdate('Ymd').'T'. gmdate('His') . "Z\r\n
                DTSTART:".$startdate."T".$startTime."00Z\r\n
                DTEND:".$enddate."T".$endTime."00Z\r\n
                SUMMARY:".$subject."\r\n
                ORGANIZER;CN=".$CFG->fullname.":mailto:".$CFG->smtpuser."\r\n
                LOCATION:".$CFG->wwwroot."\r\n
                DESCRIPTION:".$body."\r\n
                ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;CN".fullname($user).";X-NUM-GUESTS=0:MAILTO:".$user->email."\r\n
                END:VEVENT\r\n
                END:VCALENDAR\r\n";
        $mail->isHTML(true);
        $mail->Subject = $subject;
        $mail->Body = $body;

        $mail->AltBody = $text; // in your case once more the $text string
        $mail->Ical = $text; // ical format, in your case $text string

        if ($mail->Send()) {
            $mail->ClearAllRecipients();
            $mail->ClearReplyTos();
            $mail->ClearCustomHeaders();
        }