I have a problem that potentially causes me to miss important email: An incoming message is automatically marked as read after a few seconds. One can watch how a new email is at first unread in the inbox and then turns to read. This problem seems to occur only for one of several IMAP accounts.
My settings are: In the viewing tab a selection "Mark all messages as read when opening a conversation" check box is unset.
What could cause this? How can I diagnose if the problem is on the server side or if Mail.app is malfunctioning?