FastMail supports the
iCalendar standard. All travel arrangements I have made in the past few years generate an email to me which I can import into the calendar (Outlook or Fastmail). All of my travel information is in the event automatically placed on my calendar from the email.
See:
https://www.fastmail.com/help/calendar/events.html#rsvp
https://www.fastmail.com/help/calend...calendars.html
Bill