Excerpts from Elias Norberg's message of 2016-04-13 16:14:12 +0200:
> I was wondering if anyone has a neat solution to dealing with .ICS-files?
> Displaying them via mailcap is simple enough - accepting or rejecting a
> meeting not so much.
> 
> How do you deal with stuff like this? Just reply with a simple "I'll be
> there / Won't be there", or something more advanced?

I worked at a company that used the calendar stuff.  Unfortunately, I
didn't find a solution to the problem you're describing.  I see there
is a program called gcalcli, a command line tool for dealing with
Google calendars.  But I'm not sure this would have worked with other
calendar systems.

This probably won't help, but I was able to get the calendar events
to display in sup without mailcap.  Attached is my ~/.sup/hooks/mime-decode.rb
file.