Hi, an Office365 user with Business Standard license has a problem in Outlook. For no apparent reason some random emails are duplicated. If one of these emails is read the copy is also read and if it is deleted the copy is also deleted. The only way to resolve this is to close and reopen Outlook and the duplicate emails will disappear. The problem recurs again on other emails after a few weeks. After reinstalling Office and recreating the OST file, we decided to replace the PC but the problem also recurred on the new PC. Has this happened to anyone yet? How did you solve it? The user uses categories a lot other than that there is nothing in particular that could cause the problem.