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 duplicates. Outlook on a Mac may not have the same options available.

1. Start the Outlook Desktop application.
2. Select the folder that you want to clean up.
3. Click the Delete drop-down and then click Clean up folders & subfolders.
4. Click Settings.
5. Scroll down to Conversation Cleanup and change the settings to what you want.
6. Click OK.
7. Click Clean up folder.
8. Items will be moved to your Deleted items folder.