Well your first mistake was obviously letting mail.com make what you felt was visually wrong into something actually wrong and actually broken.

I am guessing you were looking for the unified folder view (View menu > view > folders > unified)

Or perhaps you have in the past used the global inbox for all POP mail accounts. I am really guessing because how you got to the point of two boxes is very relevant here. Like did the upgrade happen and you were asked to set up your accounts all over again?

Not having a spam or a sent folder would be entirely expected for a newly added account for example, because neither has actually been needed so do not exist yet.

Perhaps you can fill in some of the blanks so I can do more than guess.

Hi Matt, Thanks for the response. I first notice a couple of days ago that I had two inboxes, each containing different emails. (Sorry that I called this IMAX rather than IMAP) The support person at mail.com insisted that I had created this situation although I have no recollection of doing that. You're right that I shouldn't have trusted him. I am getting some emails in the new Thunderbird installation but when I delete them there they still exist on mail.com. I saved the web page with instructions on changing from POP to IMAP and I think this is what I should do but I thought I'd check with you first. One thing that confused me is the long time delay between when a message appears in mail.com and later shows up in Thunderbird, but I suppose this is normal.

I sure appreciate your help.

Larry