From 00cf16c6553bf09e914d0b0aa1c3e2d08533d326 Mon Sep 17 00:00:00 2001
From: Jonas Heinrich <heinrich@synyx.net>
Date: Mon, 23 Jan 2023 17:29:43 +0100
Subject: [PATCH] Reschedule mail delivery if change to event is significant

---
 lib/CalDAV/Schedule/Plugin.php | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/CalDAV/Schedule/Plugin.php b/lib/CalDAV/Schedule/Plugin.php
index 3cc360f1d4..70c4534b8b 100644
--- a/lib/CalDAV/Schedule/Plugin.php
+++ b/lib/CalDAV/Schedule/Plugin.php
@@ -638,7 +638,13 @@ protected function processICalendarChange($oldObject, VCalendar $newObject, arra
                             if ($message->scheduleStatus) {
                                 $attendee['SCHEDULE-STATUS'] = $message->getScheduleStatus();
                             }
-                            unset($attendee['SCHEDULE-FORCE-SEND']);
+                            
+                            // Reschedule when change to an existing event is significant,
+                            // otherwise unset SCHEDULE-FORCE-SEND. Respecting RFC 6638 3.2.8.
+                            if (!(isset($oldObject) && $message->significantChange)) {
+                                unset($attendee['SCHEDULE-FORCE-SEND']);
+                            };
+
                             break;
                         }
                     }