Avoid mail notifications on superfluous changes

Fixes #3790

NEWS

@@ -26,6 +26,7 @@ Bug fixes
  - [web] added missing options to subscribed calendars (#3863)
  - [web] fixed resource conflict error handling (403 vs 409 HTTP code)
  - [web] restored immediate deletion of messages (without moving them to the trash)
+ - [web] avoid mail notifications on superfluous event changes (#3790)
  - [eas] improve handling of email folders without a parent
  - [eas] never send IMIP reply when the "initiator" is Outlook 2013/2016
  - [core] only consider SMTP addresses for AD's proxyAddresses (#3842)

SoObjects/Appointments/SOGoAppointmentObject.m

@@ -890,12 +890,13 @@ inRecurrenceExceptionsForEvent: (iCalEvent *) theEvent
                             toAttendees: addedAttendees
                                withType: @"calendar:invitation"];
     }
-      
-      [self sendReceiptEmailForObject: newEvent
-                       addedAttendees: addedAttendees
-                     deletedAttendees: deletedAttendees
-                     updatedAttendees: updatedAttendees
-                            operation: EventUpdated];
+
+  if ([changes hasChanges])
+    [self sendReceiptEmailForObject: newEvent
+                     addedAttendees: addedAttendees
+                   deletedAttendees: deletedAttendees
+                   updatedAttendees: updatedAttendees
+                          operation: EventUpdated];
 
   return nil;
 }