These instructions may help remove duplicates from Outlook within Windows that could be caused by the email migration. The tool is limited, so it may not remove all duplications. Outlook on a Mac may not have the same options available.
- Open Outlook Desktop application.
- Select the folder that you want to clean up.
- Select the Delete drop down and choose Clean up folders & subfolders.
- Click on Settings.
- Scroll down to Conversation Cleanup and evaluate if these settings are appropriate. Change as necessary.
- Click OK.
- Click Clean up folder.
- Items will be moved to your Deleted items folder.