Calendar invitations via email: How to update the participation status?

I’m using nextcloud-20.0.1, mail-1.6.0 and calendar-2.1.2. I’m using the web ui only.

Here is what I do:

  1. Create a new appointment within calendar -> an invitation email is sent out to the participant
  2. Accept the invitation be means of the receiving application. For roundcube, this means using the upper part of the message - see screenshot below
  3. An acceptance mail is sent back to the mail account of the user who created the appointment
  4. The acceptance mail shows up within the mail application of nextcloud

That’s all fine so far. Now I’d like to update the participation status of the appointment based on this mail but this doesn’t seem to be possible. Or is it?

where? in the original invitation email?