I have noticed that if calendar synchronization is turned on even on a single users mobile device, CPU usage spikes up to 80% due to the sheer amount of requests performed per second.
Is there a way to turn off calendar synchronization as a feature for Mail-in-a-box?
For the Calendar sync are you doing this via Z-Push or Caldav?
You could try to disable the calendar app via the command line
sudo -u www-data php occ app:disable
Not sure if this will cause other problems though, hopefully someone with more nextcloud experience can chime in.
Just tried this solution. Seems to have worked! Let’s see what happens in long-term