Users who have Office 365 will have duplicate emails if they use a POP account.
First, disable Office updates. Inside Outlook, go to File => Office Account => Update Options (dropdown) => Disable Updates.
Close out of all Office applications that are open.
Now open an elevated command prompt (Search => cmd => CTRL+SHIFT+Enter) and run the following:
C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe /update user updatetoversion=16.0.6366.2068
- This reverts you to the February build, you will need to re-enable updates in the future once MS comes up with a fix for this.