After importing data from PST to Exchange Online account, users can't modify items imported to calendar

Question

I've got a problem with users. After importing PST files to Exchange Online accounts, they have a problem with calendars. whenever they want to modify an item, that has been created on old system, it says, that they don't have required rights to manage this item (as they didn't create it). using set-mailboxfolderpermission to modify permissions to calendar folder didn't do the trick (unless i have to grant those to Anonymous user?). the import was done from my admin-account (if that is important)

Answer 1

This is by design. From Microsoft:

When meetings are exported to or imported from an Outlook Personal Folder or Outlook Data (.pst) file, the GlobalObjectID (GOID) property of the meeting is not included. When you copy and paste meetings from one calendar to another, Outlook generates new GlobalObjectID values for the meetings that are newly created.

The GlobalObjectID is a unique identifier for a meeting. All meeting invitations, responses, and updates that are associated with any single meeting contain the same GlobalObjectID. Outlook does not create meetings that have duplicate GlobalObjectID properties. To do this, Outlook excludes the property during import and export and generates a new GlobalObjectID value when a meeting is copied. This prevents anyone who imported or copied your meetings from assuming the organizer role and sending updates for meetings that you own.

So in a nutshell, the new mailbox/user isn't the "organizer" of the meeting and therefore can't modify it. The only solution is to recreate the items. I worked with Microsoft support on this very issue several months ago.