For a ceratain account in our organisation mails are not being sent but automatically moved to the concepts folder. The account has not reached it's maximum, I know this is default behavior when this happens.
Strange is also that it states 7 messages are in the concepts folder, but I can see only 6 massages. Maybe this leads to the root cause?
All actions are performed through the Outlook Web interface so it is not a third party mailprogram causing the problem.