I have seen this question posted recently, but none of the suggestions are working.  I have Gmail and recently the sent items disappeared in outlook.  I went in and changed the IMAP setting to keep copies on the server and when I did that, all sent emails showed up under the [Gmail] directory with me (Sender) in the header for every email.  I removed the account from outlook and set it up again.  When the account starts up, the sent items folder is initially populated then everything disappears in about 30 seconds.  Additionally, and I am not sure if it is related, there is a folder under [Gmail] that is labeled with only an apostrophe and has the email folders that I created inside.  I cannot option-click on a folder and clear the cache so that is confusing as well.  It is annoying to have to access my account via webmail in order to look up a sent item.  Please help!