Applicable to Web Client, iOS and Mobile Web Client as well as Schedule Changes Emails.
Sometimes it can be useful to have an "Internal" PM type, where you can add information and book Users, but they must not be able to see that PM Booking.
This can be done by simply choosing which events should be shown (and will be included in Schedule Changes Emails...) in Toolbox > Server Setup:
Anne booked as Unavailable...
Can't see event in Web Client, iOS, Mobile Web Client.
Also excluded from Schedule Notification Email. Booked another event and modified one.... after another update of email send out, the "Unavailable" is excluded from here.