Please provide more detail. What happens when you click a message in the message list pane?

David, thank you for your question. I went to ChatGPT and it walked me through every step and it worked, not only with the one-click problem but with a half dozen other issues. I have a new HP All-in-one computer to get Windows 11. I still can't send email from Thunderbird on my computer. My cell can receive and send. My computer can only receive. I am in touch with Cybermesa but they are in the middle of a new email restructure and even their mailbox is full. Usually one gets an actual tech support person with no delay or a quick call-back. When I try to send email I am asked to enter my password and then I receive another pop-up that says it has timed out, which it hasn't. I tried turning off and restarting computer. I think you are going to advise me to just be patient with the Cybermesa tech team, but I thought you might have a quick fix. Many thanks!!!

and I would guess your shiny new computer came with a shiny new antivurs. If it is other than defender, which is part of windows ask yourself, what is so wrong with the product they need to resort to preinstalled to flow it.

My understanding is HP flog McAfee with new computers and it simply does not work with email clients that value security. I guess HP get it for free cause it is not a good product unless the only thing you use your computer for is web browsing.

there are procedures available from McAfee to reduce your connection security to work with their product, there are also options to simply prevent the McAfee product scanning secure connections. Neither are ideal.

If you have the release version of Thunderbird go to account settings on the menu and in server settings check what it says under the Connection security box. It offers things like test or sometime get certificate if the solution is to allow a non standard certificate generated and produced by your antivirus product. But what it says there will offer further clues as to t6he exact problem.