I am sending invites in outlook, but when the date passes from October, in case it enters summer time, the Outlook itself adds an extra hour.
<?php
function sendIcalEvent ($ from_name, $ from_address, $ to_name, $ to_address, $ startTime, $ endTime, $ subject, $ description, $ location) { $ domain = 'exchangecore.com';
//Create Email Headers
$mime_boundary = "----Meeting Booking----".MD5(TIME());
$headers = "From: ".$from_name." <".$from_address.">\n";
$headers .= "Reply-To: ".$from_name." <".$from_address.">\n";
$headers .= "MIME-Version: 1.0\n";
$headers .= "Content-Type: multipart/alternative; boundary=\"$mime_boundary\"\n";
$headers .= "Content-class: urn:content-classes:calendarmessage\n";
//Create Email Body (HTML)
$message = "--$mime_boundary\r\n";
$message .= "Content-Type: text/html; charset=UTF-8\n";
$message .= "Content-Transfer-Encoding: 8bit\n\n";
$message .= "<html>\n";
$message .= "<body>\n";
$message .= '<p>Caro '.$to_name.',</p>';
$message .= '<p>'.$description.'</p>';
$message .= "</body>\n";
$message .= "</html>\n";
$message .= "--$mime_boundary\r\n";
$ical = 'BEGIN:VCALENDAR' . "\r\n" .
'PRODID:-//Microsoft Corporation//Outlook 10.0 MIMEDIR//EN' . "\r\n" .
'VERSION:2.0' . "\r\n" .
'METHOD:REQUEST' . "\r\n" .
'BEGIN:VTIMEZONE' . "\r\n" .
'TZID:Brasilia' . "\r\n" .
'BEGIN:STANDARD' . "\r\n" .
'DTSTART:20181212T073000Z' . "\r\n" .
'TZOFFSETFROM:-0500' . "\r\n" .
'TZOFFSETTO:-0300' . "\r\n" .
'TZNAME:EDT' . "\r\n" .
'END:STANDARD' . "\r\n" .
'BEGIN:DAYLIGHT' . "\r\n" .
'DTSTART:20181212T073000Z' . "\r\n" .
'RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=2SU;BYMONTH=3' . "\r\n" .
'TZOFFSETFROM:-0500' . "\r\n" .
'TZOFFSETTO:-0300' . "\r\n" .
'TZNAME:EDT' . "\r\n" .
'END:DAYLIGHT' . "\r\n" .
'END:VTIMEZONE' . "\r\n" .
'BEGIN:VEVENT' . "\r\n" .
'ORGANIZER;CN="'.$from_name.'":MAILTO:'.$from_address. "\r\n" .
'ATTENDEE;CN="'.$to_name.'";ROLE=REQ-PARTICIPANT;RSVP=TRUE:MAILTO:'.$to_address. "\r\n" .
'LAST-MODIFIED:' . date("Ymd\TGis") . "\r\n" .
'UID:'.date("Ymd\THis", strtotime($startTime)).rand()."@".$domain."\r\n" .
'DTSTAMP:'.date("Ymd\THis"). "\r\n" .
'DTSTART;TZID="Brasilia":'.date("Ymd\THis", strtotime($startTime)). "\r\n" .
'DTEND;TZID="Brasilia":'.date("Ymd\THis", strtotime($endTime)). "\r\n" .
'TRANSP:OPAQUE'. "\r\n" .
'SEQUENCE:1'. "\r\n" .
'SUMMARY:' . $subject . "\r\n" .
'LOCATION:' . $location . "\r\n" .
'CLASS:PUBLIC'. "\r\n" .
'PRIORITY:5'. "\r\n" .
'BEGIN:VALARM' . "\r\n" .
'TRIGGER:-PT15M' . "\r\n" .
'ACTION:DISPLAY' . "\r\n" .
'DESCRIPTION:Reminder' . "\r\n" .
'END:VALARM' . "\r\n" .
'END:VEVENT'. "\r\n" .
'END:VCALENDAR'. "\r\n";
$message .= 'Content-Type: text/calendar;name="meeting.ics";method=REQUEST'."\n";
$message .= "Content-Transfer-Encoding: 8bit\n\n";
$message .= $ical;
echo date("Ymd\THis", strtotime($startTime));
echo "<br>";
$mailsent = mail($to_address, $subject, $message, $headers);
return ($mailsent)?(true):(false);
}