[GH-ISSUE #463] Two Outlooks with two CalDavSynchronizers on a shared calender do play ping-pong (SEQUENCE is increasing) #448

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opened 2026-02-25 20:31:40 +03:00 by kerem · 0 comments

kerem commented

2026-02-25 20:31:40 +03:00

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Originally created by @winnieXY on GitHub (Jan 15, 2026).
Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/463

Hey,

I'm using a nextcloud with a shared calender for me and my wife. We both sync the shared calender into our outlook using CalDavSynchronizer.

To prevent Timezone Pingpong i switched on the option "Create events on server with downloaded IANA timezones" and selected our timezone.

However this does not prevent the ping-pong (and thus notifications about changed appointments from nextcloud).
This happens for all appointments within the calender.

Here is one example of such a appointment - once synced by me, once synced by my wife:

After my CalDavSynchronizer synced:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//ddaysoftware.com//NONSGML DDay.iCal 1.0//EN
BEGIN:VTIMEZONE
LAST-MODIFIED:20251211T094730Z
TZID:Europe/Berlin
TZURL:https://www.tzurl.org/zoneinfo-outlook/Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:DAYLIGHT
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
TZNAME:CEST
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:CET
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CLASS:PUBLIC
DTEND;VALUE=DATE:20251215
DTSTAMP:20260115T082251Z
DTSTART;VALUE=DATE:20251212
PRIORITY:5
SEQUENCE:743
SUMMARY:Test Appointment
TRANSP:TRANSPARENT
UID:3e99ec25-1c42-47a2-876d-d1d0b4804d0b
X-MICROSOFT-CDO-BUSYSTATUS:FREE
END:VEVENT
END:VCALENDAR

after the caldavsynchronizer of my wife synced:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//ddaysoftware.com//NONSGML DDay.iCal 1.0//EN
BEGIN:VTIMEZONE
LAST-MODIFIED:20251211T094730Z
TZID:Europe/Berlin
TZURL:https://www.tzurl.org/zoneinfo-outlook/Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:DAYLIGHT
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
TZNAME:CEST
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:CET
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CLASS:PUBLIC
DTEND;VALUE=DATE:20251215
DTSTAMP:20260115T080954Z
DTSTART;VALUE=DATE:20251212
PRIORITY:5
SEQUENCE:742
SUMMARY:Test Appointment
TRANSP:TRANSPARENT
UID:3e99ec25-1c42-47a2-876d-d1d0b4804d0b
X-MICROSOFT-CDO-BUSYSTATUS:FREE
END:VEVENT
END:VCALENDAR

The ping-pong is also very well visible within the apache access log:

195.145.170.173 - - [14/Jan/2026:13:11:50 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
87.191.45.66 - - [14/Jan/2026:13:43:53 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
195.145.170.173 - - [14/Jan/2026:14:43:09 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
94.31.74.44 - - [14/Jan/2026:16:25:49 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
147.161.235.1 - - [15/Jan/2026:07:07:43 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
87.191.45.66 - - [15/Jan/2026:08:08:40 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"
147.161.235.1 - - [15/Jan/2026:08:22:51 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6"

The only difference is the DTSTAMP and a increased SEQUENCE (which will trigger the notification mail from nextcloud).

would it be possible to add a option to caldavsynchronizer to stop updating the appointment if just the DTSTAMP has changed (or updated the DTSTAMP without increasing SEQUENCE?

We both have this setup:

Windows: Win 11
Outlook 365
CalDavSynchronzier 4.6.0
Nextcloud 31

If needed I could get some debug logs.

Originally created by @winnieXY on GitHub (Jan 15, 2026). Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/463 Hey, I'm using a nextcloud with a shared calender for me and my wife. We both sync the shared calender into our outlook using CalDavSynchronizer. To prevent Timezone Pingpong i switched on the option "Create events on server with downloaded IANA timezones" and selected our timezone. However this does not prevent the ping-pong (and thus notifications about changed appointments from nextcloud). This happens for _all_ appointments within the calender. Here is one example of such a appointment - once synced by me, once synced by my wife: After my CalDavSynchronizer synced: ``` BEGIN:VCALENDAR VERSION:2.0 PRODID:-//ddaysoftware.com//NONSGML DDay.iCal 1.0//EN BEGIN:VTIMEZONE LAST-MODIFIED:20251211T094730Z TZID:Europe/Berlin TZURL:https://www.tzurl.org/zoneinfo-outlook/Europe/Berlin X-LIC-LOCATION:Europe/Berlin BEGIN:DAYLIGHT DTSTART:19700329T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 TZNAME:CEST TZOFFSETFROM:+0100 TZOFFSETTO:+0200 END:DAYLIGHT BEGIN:STANDARD DTSTART:19701025T030000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZNAME:CET TZOFFSETFROM:+0200 TZOFFSETTO:+0100 END:STANDARD END:VTIMEZONE BEGIN:VEVENT CLASS:PUBLIC DTEND;VALUE=DATE:20251215 DTSTAMP:20260115T082251Z DTSTART;VALUE=DATE:20251212 PRIORITY:5 SEQUENCE:743 SUMMARY:Test Appointment TRANSP:TRANSPARENT UID:3e99ec25-1c42-47a2-876d-d1d0b4804d0b X-MICROSOFT-CDO-BUSYSTATUS:FREE END:VEVENT END:VCALENDAR ``` after the caldavsynchronizer of my wife synced: ``` BEGIN:VCALENDAR VERSION:2.0 PRODID:-//ddaysoftware.com//NONSGML DDay.iCal 1.0//EN BEGIN:VTIMEZONE LAST-MODIFIED:20251211T094730Z TZID:Europe/Berlin TZURL:https://www.tzurl.org/zoneinfo-outlook/Europe/Berlin X-LIC-LOCATION:Europe/Berlin BEGIN:DAYLIGHT DTSTART:19700329T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 TZNAME:CEST TZOFFSETFROM:+0100 TZOFFSETTO:+0200 END:DAYLIGHT BEGIN:STANDARD DTSTART:19701025T030000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZNAME:CET TZOFFSETFROM:+0200 TZOFFSETTO:+0100 END:STANDARD END:VTIMEZONE BEGIN:VEVENT CLASS:PUBLIC DTEND;VALUE=DATE:20251215 DTSTAMP:20260115T080954Z DTSTART;VALUE=DATE:20251212 PRIORITY:5 SEQUENCE:742 SUMMARY:Test Appointment TRANSP:TRANSPARENT UID:3e99ec25-1c42-47a2-876d-d1d0b4804d0b X-MICROSOFT-CDO-BUSYSTATUS:FREE END:VEVENT END:VCALENDAR ``` The ping-pong is also very well visible within the apache access log: ``` 195.145.170.173 - - [14/Jan/2026:13:11:50 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 87.191.45.66 - - [14/Jan/2026:13:43:53 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 195.145.170.173 - - [14/Jan/2026:14:43:09 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 94.31.74.44 - - [14/Jan/2026:16:25:49 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 147.161.235.1 - - [15/Jan/2026:07:07:43 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 87.191.45.66 - - [15/Jan/2026:08:08:40 +0000] "PUT /remote.php/dav/calendars/user2/gemeinsamer-kalender_shared_by_user1/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" 147.161.235.1 - - [15/Jan/2026:08:22:51 +0000] "PUT /remote.php/dav/calendars/user1/gemeinsamer-kalender/3e99ec25-1c42-47a2-876d-d1d0b4804d0b.ics HTTP/1.1" 204 - "-" "CalDavSynchronizer/4.6" ``` The only difference is the DTSTAMP and a increased SEQUENCE (which will trigger the notification mail from nextcloud). would it be possible to add a option to caldavsynchronizer to stop updating the appointment if _just_ the DTSTAMP has changed (or updated the DTSTAMP without increasing SEQUENCE? We both have this setup: - Windows: Win 11 - Outlook 365 - CalDavSynchronzier 4.6.0 - Nextcloud 31 If needed I could get some debug logs.