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[JMAP] Re: [calsify] VTIMEZONE (was: Re: Re: Working Group Last Calls: the JMAP Calendars/JSCalendar group=

Mauro De Gennaro <mauro@stalw.art> Mon, 24 August 2026 14:41 UTC

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From: Mauro De Gennaro <mauro@stalw.art>
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Date: Mon, 24 Aug 2026 16:41:11 +0200
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Subject: [JMAP] Re: [calsify] VTIMEZONE (was: Re: Re: Working Group Last Calls: the JMAP Calendars/JSCalendar group=
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> An attempt was already made to rid ourselves of passing VTIMEZONE around and I don’t think it has gained much traction: https://datatracker.ietf.org/doc/rfc7809/

I was thinking of a document that updates iCalendar directly. It could even carry Informational status, encouraging implementers to stop generating and parsing VTIMEZONE, though updating the spec directly seems more correct, since the current text mandates that iCalendar include VTIMEZONE.


> I agree that deprecating embedded VTIMEZONE in iCalendar would be the right thing. But writing a document is unlike to make that happen, unless either the document codifies the current state of the VTIMEZONE handling by the major players, or they are willing to update their implementations.
> It would be great to systematically assess the current state how clients and servers deal with VTIMEZONE (or lack of) currently, though. My understanding is that most implementations already ignore embedded VTIMEZONEs if the TZID is an IANA name and instead use the current IANA timezone rules for that timezone name.


Based on a bug report I received last week, it looks like Outlook still relies on VTIMEZONE to correctly render dates. A user reported that an event with DTSTART set to a TZID of "Europe/Berlin" and no VTIMEZONE was displayed one hour off in Outlook.

I know deprecating VTIMEZONE will take time and might never gain traction among the major players, but I believe this document will be needed at some point


Best,
Mauro

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