Hi @Marko T
Welcome to our forum!
For better research, please provide more details about this case:
What version of your Outlook client is?
Did this happen by accident? Or is this the case with all mails?
Try the following possible solutions:
1.Check your Outlook client version to make sure you have updated to the latest version.
2.Select File > Options > Advanced. Under Outlook panes, select Reading Pane. You can change how quickly messages are marked as read or change how and when messages are marked as read, then see if the changes take effect.
3.Corrupted Outlook views might cause issues like this. To make your view settings go back to the default, you could try the /cleanviews command (Press Win + R, type “Outlook.exe /cleanviews”, press Enter) and see if there is any difference. If necessary, remember to back up your views first.
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