Dedicated two-way Google Calendar sync.

Yes. Cleanmail has dedicated two-way Google Calendar sync. It puts the dates from your school and activity email on your Google Calendar, and when you edit or delete one of those events in Google Calendar, the change comes back to Cleanmail automatically, usually within seconds.

It leaves Cleanmail too and goes to Cleanmail's Trash, labeled Deleted in Google Calendar. A later email from the school won't put it back on your calendar. If you change your mind, restore it in either Google Calendar or Cleanmail and it comes back in both.

The most recent edit wins. Cleanmail never wins just because it's Cleanmail.

Title, date, time, and location, plus deletes and restores. Edits made in the iPhone Calendar app sync back too when it's showing your Google calendar.

The one you pick, called your main calendar. You choose it during setup and can switch it anytime in Settings. Events you create yourself in Google Calendar show up inside Cleanmail too, labeled Google Calendar.

No. Cleanmail only asks Google for permission to add and edit events. It never asks to delete or manage your calendars, and you can see the exact permission on Google's consent screen when you connect.