Hi Wouter,

ical support for events with multiple days is patchy at best across the range of email clients and many versions of Outlook don't support it at all. If you look at the actual contents of the ical file you should see the BEGIN:VEVENT...END:VEVENT blocks in there defining the multiple dates, unfortunately they are rarely read properly by the email/calendar clients.

For this reason there is a little-known Face To Face configuration setting

Site Administration -> Plugins -> Activities -> Face-to-face -> One message per day

This gets around the problems with most email clients by sending an emails with a single-day ical attachment for each day of the event so for example when this setting is turned on:

A facetoface session with two dates on the 4th July and 9th July, when booked the user will receive two emails, each containing one ical attachment, one for the 4th and one for the 9th.

So if you are doing a lot of multi-day face-to-face sessions, it may be best to turn this setting on. This is a bit clunky but there is little we can do about the poor support for multi-day events in most email clients, even though it is part of the ical standard definition.