This is a tutorial on adding calendar permissions in Office 365 for your users via Powershell. You can add permissions onto a specific mailbox, or you can add it onto a security group.
Office 365 Calendar Permissions
The first is step is to launch Windows Powershell. I recommend running it as administrator. Instructions on installing Windows Powershell.
Run the following command to login to 365 via Powershell and login with your 365 admin credentials.
$LiveCred = Get-Credential
Now you need to create a new session.
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $LiveCred -Authentication Basic -AllowRedirection
Now we need to import the session.
These are the available roles:
Now run the following command. In this example below, user2 would be able to open user1 calendar and edit it.
Add-MailboxFolderPermission -Identity firstname.lastname@example.org:\calendar -user email@example.com -AccessRights Editor
Also see this 365 script for setting calendar permissions: Set Calendar Permission in Office 365 Exchange Online.
If the above information helped you, make sure to check out our official Office 365 Migration Guide.