iCal outlook email compatibility problems - email

Question

I'm trying to generate an iCal file with multiple VEVENTs. I want to achieve one .ics-file, which has multiple appointments in it. It is important that these are not all-day appointments. So far, my generated file looks like this:
BEGIN:VCALENDAR
VERSION:2.0
PRODID: *** CENSORED ***
METHOD:REQUEST
X-MS-OLK-FORCEINSPECTOROPEN:1
BEGIN:VEVENT
UID:uuid-e4a9084f-91ea-4bc7-9bc0-3b2d6bec9030
DTSTART:20211122T070000Z
SEQUENCE:1
TRANSP:TRANSPARENT
STATUS:CONFIRMED
DTEND:20211122T160000Z
SUMMARY: TEXT
ATTENDEE;CN=FirstName_LastName;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;RSVP=FALSE;PA
RTSTAT=NEEDS-ACTION:MAILTO:*** CENSORED ***
CLASS:PUBLIC
DESCRIPTION: TEXT
ORGANIZER;CN=*** CENSORED ***:MAILTO:*** CENSORED ***
X-MICROSOFT-CDO-BUSYSTATUS:FREE
X-MICROSOFT-CDO-INTENDEDSTATUS:FREE
DTSTAMP:20211027T141024Z
LAST-MODIFIED:20211027T141024Z
END:VEVENT
BEGIN:VEVENT
UID:uuid-e4a9084f-91ea-4bc7-9bc0-3b2d6bec9030
DTSTART:20211123T070000Z
SEQUENCE:1
TRANSP:TRANSPARENT
STATUS:CONFIRMED
DTEND:20211123T160000Z
SUMMARY: TEXT
ATTENDEE;CN=FirstName_LastName;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;RSVP=FALSE;PA
RTSTAT=NEEDS-ACTION:MAILTO:*** CENSORED ***
CLASS:PUBLIC
DESCRIPTION: TEXT
ORGANIZER;CN=*** CENSORED ***:MAILTO:*** CENSORED ***
X-MICROSOFT-CDO-BUSYSTATUS:FREE
X-MICROSOFT-CDO-INTENDEDSTATUS:FREE
DTSTAMP:20211027T141024Z
LAST-MODIFIED:20211027T141024Z
END:VEVENT
END:VCALENDAR
So far so good. When I import this iCal-file to Google Calendar or even Outlook, both appointments are added correctly. The problem is when I attach the .ics-file to an email. Google Mail recognizes the attachment as as appointment and lets me Accept/Decline it in the email.
When I open the exact same email in Outlook, Outlook doesnt even recognize the attachment as an appointment. I also have the problem, that only one VEVENT, the first one, is added to the outlook calendar.
Is there something special about iCal attachments for Outlook? Can I do something to improve the compatiblity?

Answer 1

Multiple events within a single METHOD:REQUEST are only permitted where they have a single UID (ie they are part of the same multi instance event. See:
https://datatracker.ietf.org/doc/html/rfc2446#section-3.2.2
If the events are conceptually related, you could consider issuing the same UID and using RDATE https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.5.2to distinguish the separate instances. It doesn't matter whether they are all day or not.
One can import multiple events as you have discovered.
Alternatively you could consider using METHOD:PUBLISH and having the user subscribe to their own personal appointments calendar if there are multiple separate events and you don't want to use RDATE.