Exchange 2025 Shared Calendar With External Users. A workround is creating an internal mailbox/mail contact for the external user and assigning calendar permission for that mailbox/mail contact, then adding this. If you have calendars that are shared with external users, this advice is expected behavior and is intended to remind you that an individual sharing policy is.
I’ve enabled external sharing in the office365 administrative area. A users shared calendar showing notifications to all users who have the calendar loaded in their local outlook installation.