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If I add this ICS file to Outlook or add it to my third party calendar app it creates an appointment at 17-dec-2017 at 11:30-12:30, which was the intention.
If I upload the ICS file in webmail, it creates the appointment at 10:30-11:30 which is one hour to early.
Is this a DST issue?
ICS file testcase:
SUMMARY:Test appointment at 11:30-12:30