PHP sends outlook appointment email

<?php 
  $to   = "other@xxxx.net"; 
  $from = "me@xxxx.net"; 
  $subj = "my test subject"; 
  $msg  = "this is the email body"; 
 
  $header = "From: " . $from . "\r\n" . 
          "MIME-Version: 1.0\r\n" . 
           "Content-Type: text/calendar;method=REQUEST"; 
 
  $txt_msg = "this is my text message, to be attached\r\n" . 
             "not much to it, eh."; 
 
  //Various ways to creat a new, random UID 
  $cal_uid = "{" . uniqid(mt_rand(), true) . "}"; 
  $cal_uid = "{" . date(&#39;Ymd&#39;).&#39;T&#39;.date(&#39;His&#39;)."-".rand()."@mydomain.com}"; 
  $cal_uid = com_create_guid(); 
 
  $cal_msg = 
"BEGIN:VCALENDAR 
PRODID:-//Microsoft Corporation//Outlook 11.0 MIMEDIR//EN 
VERSION:2.0 
METHOD:REQUEST 
BEGIN:VEVENT 
ORGANIZER:MAILTO:name 
DTSTART:20090901T170000Z 
DTEND:20090901T035959Z 
UID:" . $cal_uid . "
LOCATION:my meeting location 
TRANSP:OPAQUE 
SEQUENCE:0 
DTSTAMP:20060309T045649Z 
CATEGORIES:Meeting 
DESCRIPTION:meeting description, line 1 of 2.\nline 2 of 2.\n\n 
SUMMARY:meeting subject 
PRIORITY:5 
X-MICROSOFT-CDO-IMPORTANCE:1 
CLASS:PUBLIC 
BEGIN:VALARM 
TRIGGER:-PT3D 
ACTION:DISPLAY 
DESCRIPTION:Reminder 
END:VALARM 
BEGIN:VTIMEZONE 
TZID:US/Central 
END:VTIMEZONE 
END:VEVENT 
END:VCALENDAR"; 
  if (mail($to, $subj, $cal_msg, $header, "")) { 
    echo "test email sent"; 
  } else { 
    echo "test email failed"; 
  } 
  ?>