You can choose which calendars are visible inside AltaMail. eg. to hide/remove Holidays
Open the app settings (View) and open the Calendar section.
Tap on "Calendars" and tap each calendar to turn it on or off.

You can also choose which calendars to print. In the Print screen, tap on "Printer Options", then tap on "Calendars". Choose the calendars to print. This will not affect the calendars that appear when viewing your calendar on the screen.