Using Classic Outlook on Windows for personal email, calendar, and contact management
By unread I meant if the msg was received in MS Outlook, then moved by a rule its likely to be then shown as read.
Have you checked the 365 on line admin that there is no rule in place?
Does this issue apply only to specific sender or subject line?
There is no rule in place.
It doesn't only happen to a specific sender or subject line, just any message that "fits in" with the other messages in a given folder. The messages that are affected can be from completely different senders and can be completely different subject matter, going to different folders. But if a certain message would always be manually filed into a certain folder, then it has recently been auto-filed into that folder without coming through the inbox. This has happened with at least 3 different messages/folders, all unrelated to each other except that they are being affected by the same issue of being auto-filed.