public function Sendmail1()
    {
        ini_set("display_errors", "1");
error_reporting(E_ALL);

        // event params
$summary = 'Summary of the event';
$venue = 'Kochi';
$start = '20140820';
$start_time = '160630';
$end = '20140820';
$end_time = '180630';

//PHPMailer
$mail = new PHPMailer();
$mail->IsSMTP();
        $mail->SMTPDebug = 0;
        $mail->SMTPAuth = TRUE;
        $mail->SMTPSecure = "ssl";
        $mail->Port = 465;
        $mail->Username = "test@gmail.com";
        $mail->Password = "test";
        $mail->Host = "smtp.gmail.com";
        $mail->Mailer = "smtp";
        $mail->SetFrom("test@office.com", "test");
        $mail->AddReplyTo("test@office.com", "test");
$mail->addAddress('user1@office.com','user');
$mail->ContentType = 'text/calendar';

$mail->Subject = "Outlooked Event";
$mail->addCustomHeader('MIME-version',"1.0");
$mail->addCustomHeader('Content-type',"text/calendar; method=REQUEST; charset=UTF-8");
$mail->addCustomHeader('Content-Transfer-Encoding',"8bit");
$mail->addCustomHeader('X-Mailer',"Microsoft Office Outlook 12.0");
$mail->addCustomHeader("Content-class: urn:content-classes:calendarmessage");
$event_id = 1234;
$sequence = 0;
$status = 'TENTATIVE';
$ical = "BEGIN:VCALENDARrn";
$ical .= "VERSION:2.0rn";
$ical .= "PRODID:-//YourCassavaLtd//EateriesDept//ENrn";
$ical .= "METHOD:REQUESTrn";
$ical .= "BEGIN:VEVENTrn";
$ical .= "ORGANIZER;SENT-BY="MAILTO:organizer@kaserver.com":MAILTO:onbehalfoforganizer@kaserver.comrn";
$ical .= "ATTENDEE;CN=them@kaserver.com;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;RSVP=TRUE:mailto:organizer@kaserver.comrn";
$ical .= "UID:".strtoupper(md5($event_id))."-kaserver.comrn";
$ical .= "SEQUENCE:".$sequence."rn";
$ical .= "STATUS:".$status."rn";
$ical .= "DTSTAMPTZID=Africa/Nairobi:".date('Ymd').'T'.date('His')."rn";
$ical .= "DTSTART:".$start."T".$start_time."rn";
$ical .= "DTEND:".$end."T".$end_time."rn";
$ical .= "LOCATION:".$venue."rn";
$ical .= "SUMMARY:".$summary."rn";
//$ical .= "DESCRIPTION:".$event['description']."rn";
$ical .= "BEGIN:VALARMrn";
$ical .= "TRIGGER:-PT15Mrn";
$ical .= "ACTION:DISPLAYrn";
$ical .= "DESCRIPTION:Reminderrn";
$ical .= "END:VALARMrn";
$ical .= "END:VEVENTrn";
$ical .= "END:VCALENDARrn";

$mail->Body = $ical;

//send the message, check for errors
if(!$mail->send()) {
$this->error = "Mailer Error: " . $mail->ErrorInfo;
echo 'okie';
} else {
$this->error = "Message sent!";
echo 'not okie';
}
    }

Notice: Undefined offset: 1 in /var/www/html/manage/libraries/phpMailer/class.phpmailer.php on line 1141

Notice: Undefined offset: 1 in /var/www/html/manage/libraries/phpMailer/class.phpmailer.php on line 1141

Notice: Undefined offset: 1 in /var/www/html/manage/libraries/phpMailer/class.phpmailer.php on line 1141

Notice: Undefined offset: 1 in /var/www/html/manage/libraries/phpMailer/class.phpmailer.php on line 1141

for($index = 0; $index < count($this->CustomHeader); $index++) {
      $result .= $this->HeaderLine(trim($this->CustomHeader[$index][0]), $this->EncodeHeader(trim($this->CustomHeader[$index][1])));

    }

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//YourCassavaLtd//EateriesDept//EN
METHOD:REQUEST
BEGIN:VEVENT
ORGANIZER;SENT-BY="MAILTO:organizer@kaserver.com":MAILTO:onbehalfoforganizer@kaserver.com
ATTENDEE;CN=them@kaserver.com;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;RSVP=TRUE:mailto:organizer@kaserver.com
UID:81DC9BDB52D04DC20036DBD8313ED055-kaserver.com
SEQUENCE:0
STATUS:TENTATIVE
DTSTAMPTZID=Africa/Nairobi:20180221T102303
DTSTART:20140820T160630
DTEND:20140820T180630
LOCATION:Kochi
SUMMARY:Summary of the event
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR