Sharing policies in Exchange Online
People in your organization may want to share calendars with individual business associates, friends, or family members. Sharing policies control how your users share their calendars with people outside your organization. The sharing policy that an admin applies to the user's mailbox determines what level of access a user can share and with whom. If you don't change anything, then all users can invite anyone with an email address to view their calendar. You may decide to apply a more restrictive policy.
An admin defines the rules that make up a sharing policy. You can specify the domains that users can share with, and the following levels of access to calendars:
Free/busy information with time only
Free/busy information with time, subject, and location
Free/busy information, including time, subject, location, and title
After you create a new sharing policy, you have to apply that policy to mailboxes before it takes effect. Sharing policies are applied to individual user's mailboxes. An admin can also disable a user's sharing policy to prevent external access to calendars.
Users share their calendar by sending an email invitation to the external user. Outlook 2010 or later or Outlook Web App can send this type of invitation. The calendar can be opened through a URL link, or can be accessed as an additional calendar folder if the external user has Outlook 2010 or later or is using Outlook Web App.
These topics will help you learn how to manage sharing policies for your Office 365 organization: