Hi Richard Yeung,
Welcome to our forum!
Does the folder under the account show the number of unread emails?
If so, it is recommended that you remove and re-add the folder as a favorite folder to see if the issue persists.
If not, it is suggested please log in to the web version to see if there is the same issue.
- If so, please check if there are some rules that affect the status of read and unread.
- If not, you may try uninstalling and reinstalling the New Outlook to see if the issue has been solved.
Hope it helps.
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