No matter what you want to do with calendars server-side in Exchange, you are going to need to become conversant in Exchange permissions. It's the devil's bargain: if you want to migrate all your calendar data and preserve its utility with guest lists and responses, then you need to be able to manage Permissions on your Exchange users.
So here we're putting out our best effort at a cookbook guide to Exchange 2013 permissions for migrations. Even though full-state calendar migrations will never be a purely cookbook operation we think this will get you there (and we have some field experience taking a couple of novices through it this way),
First: GLOBAL ADMINISTRATOR rights are NOT enough. These rights give you administration rights over Exchange / Active Directory, but they do not give you the rights to access mailboxes – which is what you will need to move in data and re-create state.
We’re going to take this in stages.
- Use REMOTE POWERSHELL to Log into Office 365
- Create a separate service account (this keeps your ADMIN function separate from your MIGRATION function)
- We call the Service Account EXSU. When you create it, make sure it is mailbox-enabled (you will be sending email on behalf of this account
- Grant EXSU three rights:
- No throttling. This is relevant (i.e., in your control) only for on-premises Exchange. For Office 365 you will need to contact your Microsoft rep and explain what you are doing and ask throttling turned off for the duration of your migration.
- FULL ACCESS to mailboxes (this makes it easy to use OWA with this account to check the results for individual users in testing and migration)
You should see this: