Share Microsoft 365 calendars with external users
It's sometimes necessary for your users to schedule meetings with people outside your organization. To simplify the process of finding mutually agreeable meeting times, Microsoft 365 enables you to make calendars available to external users. These are people who need to see free and busy times for users in your organization, but don't have user accounts for your Microsoft 365 organization.
As the admin, you can enable calendar sharing for all users in your organization. Once sharing is enabled, users can use Outlook Web App to share their calendars with anyone inside or outside the organization. People inside the organization can view the shared calendar along with their own calendar. People outside the organization will be sent a URL that they can use to view the calendar. Users decide when to share, how much to share, and when to keep their calendars private.
If you want to share calendars with an organization that uses Exchange Server 2013 (an on-premises solution), the Exchange administrator will need to set up an authentication relationship with the cloud. This is known as "federation" and must meet minimum software requirements. See Sharing for more information.
Enable calendar sharing using the Microsoft 365 admin center
In the admin center, go to Settings > Org Settings.
On the Services tab, select Calendar.
On the Calendar page, choose whether you want to let users share their calendars with people outside of your organization who have Microsoft 365 or Exchange. Choose whether you want to allow anonymous users (users without logon credentials) to access calendars via an email invitation.
Choose what type of calendar information to make available to users. You can allow all information, or limit it to time only or time, subject, and location only.
Invite people to access calendars
Once sharing is enabled, calendar owners can extend invitations to specific users. See Sharing your calendar in Outlook Web App for instructions.