[kronolith] Event cancelation-notification sent when deleting an event from a CalDAV client

[Tom Huerlimann]

Hi all

I'm runing Horde Groupware Webmail Edition 5.2.22 / Calendar (kronolith)
4.2.24 / Horde_ActiveSync 2.39.3.

I found out, when i delete an event with an CalDAV client and sync the
changes, the Kronolith/itip application of the horde installation is sending
out an notification to all attendees and maybe the organizer as well, that
the event was canceled.

It happend that i've deleted an event from outlook with many
hunderd-thousend of attendees. I have selected in outlook not to send a
notification - so the exchange server behind did not send out any
notification but the sync-task of my CalDAV interface has synced the
cancelation with my horde server and has generated hunderd-thousands of
cancelation-notifications. Every attendee received a
cancelation-notification and the mail-distribution group, contain the same
receipients, did also receive the message. You can imagine that this started
a never seen mail-flood...

I found a couple of informations on the web about to disable itip
notifications when doing CalDAV syncs, but i was unable to change this
behaviour with the informations i found.

Already tested:

a)
https://features.cpanel.net/topic/option-to-suppress-automated-itip-notifica
tions-when-synchronising-caldav
Result: Without success, cancelation-notifications are still going out.

b) https://bugs.horde.org/ticket/14157
Result: Found some code samples in the github, did apply those (old?)
snippets but that did not work. Instead of fixing the problem, Kronolith was
not able to display the calendar anymore.
I assume this code snippets are not valid for my version anymore.

c) https://bugs.horde.org/ticket/14135
Result: Useless because Outlook (clients) is/are blamed, but Outlook is not
the root cause here.

My question is: Is there a easy way to modify a file, that i become able to
prevent Horde/Kronolith/itip from sending  out cancelation-notifications
when a event is deleted specially via CalDAV?

Have a nice weekend everybody.

Best regards
   Tom