InformationThe macOS built-in Calendar.app _MUST_ be disabled as this application can establish a connection to non-approved services. This rule is in place to prevent inadvertent data transfers.
Some organizations allow the use of the built-in Calendar.app for organizational communication. Information System Security Officers (ISSOs) may make the risk-based decision not to disable the macOS built-in Mail.app to avoid losing this functionality, but they are advised to first fully weigh the potential risks posed to their organization.
SolutionThis is implemented by a Configuration Profile.
mobileconfig profile info: