Outlook Inbox – losing emails

I am losing email from my inbox that is over a week old.  They are not in the deleted folder.  I have an IMAP account set up with Time Warner.  I have checked all folder filters and none of them are on.  This issue started a few weeks ago.  I also see that under "organize" tab, the folder "permissions" and "options" tabs are blanked out and cannot be opened.  I am operating with a MAC.  Thanks for any information that would resolve this issue.