Click on the DATE header to sort by date. Click DATE a second time to reverse the sort order.

Thank you but I'm looking for an AUTOMATIC solution. If I have to click DATE twice, I might as well click the scroll bar.

I cannot understand why it should be thought that, by default, initiating the Get Mail function should result in the output of that function being hidden!

It is set it and forget it. Once you get the sort set like you want it will stay there. This is how all Thunderbird options work. However it is set when you close Thunderbird is how it will open next time.