Open the Inbox folder. If you are using the Views Bar, then look near the
upper right corner. Does it say "Hide Read Messages" or "Show All
Messages"? You want the latter setting for what is known as the 'current view'.
Each folder saves its current view setting, so check that setting in
every folder.
If you are not using the Views Bar, you can get to the same setting by going
to View, Current View.
