OE6: Messages missing fm Inbox

Several hundreds of our email mssg fm Feb06 to 6 of July 06 are missing, some of these are very important mssg. Our last back-up was made on June 22, so we will still be missing messages fm June 22 to July 6. I have checked the deleted items folder and can confirm that it is not there. The messages in the sent folder seems to be intact. I am not sure if we have unintentionally selected an option that lead to the above mentioned scenario but I don’t think so. Some people suggested that the emails could have been auto-archived but the strangest part is that our messages fm 2005 are still in the inbox. Also being a small company we do not have an IT department. Moreover we do not have our own server. Can someone help us here? Thanks in advance.