I have been using Thunderbird about 2 months on an Ubuntu Linux laptop, and just noticed that there is nothing in my inbox that is older than 2 weeks even though I have not manually deleted messages.. My ISP server is NOT deleting messages. I have looked at the Thunderbird preferences and I have set everything I could find to "Do not delete".. I am running Thunderbird 45.2.0 and Firefox 48.0

Any ideas or suggestions??