I recently performed a POP3 to Exchange Online migration. Beyond some long syncing issues with large PST's, it was a smashing success.
I do have a few users who get duplicate calendar reminders. One user did have his old PST attached when he wanted to verify his PST migrated to Exchange. Removed it and it seemed to fix his problem. Another user, though, still gets duplicate reminders for the same meeting. I checked to see if it may be a old shared event before going to exchange and it wasn't. Not sure where else to look. How can I stop the duplicate reminder?