Loaded the new OS this morning. First thing was it drug into my active new mail folder about 1400 old Emails from the deleted mail folder, which I had not deleted (apparently, when I should have!). So I deleted everything from my in box and then from my deleted mail folder, but after a few minutes this stuff still keeps coming back. Check with my ISP (Insight Broadband) and I had only one Email in the active queue.
So, things are not being deleted, or, if they really are, some stuff is lurking in some unknown location.
How can I clean up this mess?