I don't know what version of Outlook you have, but this sounds like what has
happened to me for a few days (WinVista, Outlook 2007), only it is the
inbox--ding! You have mail--no msg. Sometime in the middle of the night, they
would show up (computer is on all the time). Checking the server directly,
there were messages there, Outlook just didn't retrieve them. Tried several
things, including disabling some of my add-ins, but finally went to
View/Current View/ and checked "Outlook data files." Then the messages all
showed up.