Configure 365 calendar permissions via PowerShell

On occasion I’ve had to adjust permissions on a calendar for a shared mailbox (note, not a resource mailbox) whereby all users need to be able to view all entries, but only edit/delete their own items. This can be achieved simply by setting the ‘Default’ user entry from the Calendar permissions tab in Outlook to Author.

When attempting to do that using the latest version of Outlook 365 (as of Jan 2022) or via the Outlook Web App, the previously present ‘Default’ and ‘Anonymous’ entries were missing from the list and the GUI had changed to just show ‘Inside My Organisation’ and a variety of options that included read-only and edit, but no fine grained options for read all/edit own. Perhaps I was missing something but I couldn’t see a way to do what I wanted (although the options are still visible in Outlook 2013), so had to resort to PowerShell.

Connect to Exchange Online, then use the following commands to check/add/edit the permissions (will also work with other folder types if you replace the :\calendar parameter as required):

Check the current permissions set on the calendar
Get-MailboxFolderPermission mailbox@domain.com:\Calendar

Set the permission for an existing defined user
Set-MailboxFolderPermission mailbox@domain.com:\Calendar -User user@domain.com -AccessRights Author

Add a new user to the permission list and grant specific permissions
Add-MailboxFolderPermission mailbox@domain.com:\Calendar -User user@domain.com -AccessRights Editor

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