In outlook.com I subscribed to my TripIt calendar feed. In outlook.com I went to Import > Subscribe, and entered the ical feed URL that I got from TripIt. The URL looks like this (redacted for privacy reasons): https://www.tripit.com/feed/ical/private/<<long
id here>>/tripit.ics. The initial import worked perfectly and all the events from TripIt show as expected in my outlook.com calendar.
However, outlook.com has not tried to refresh the feed for two days now, and, consequently, changes are not shown in outlook.com. Now, other software in which I imported the exact same feed, e.g. the OS X calendar app and my Google calendar, do see the updates
just fine. Only outlook.com does not refresh the feed, at least not in over 48 hours now.