Great stuff. So when you log on to webmail now they may all be "gone". You can copy from your machine now straight to memory stick as well, in case your hard drive goes or anything. Which was your original plan anyway
You dont need to uninstall.
Add a new account POP3 then remove the IMAP one.
https://itstillworks.com/change-thunderbird-imap-pop-server-21837.html
You have forwarded all the mail to another account just in case yeah?
When you add the Pop3 it will download all your emails to your machine and...
Ok cool
I would do 2 things bg
I would select ALL the emails you want to keep and forward them to your outlook.com address
A rudimentary back up...
Then i would install outlook on one of your devices, a pc or laptop
In this instance, assuming you wont be paying talktalk to keep your emails...
Yes but you arent answering simple questions to help people try and help you, like are you using a web browser to access your talktalk emails or do you have an email program connected to it. I honestly think that its worth finding someone local to you, bite the bullet and pay someone for...
Bg do you mean forward them to your outlook.com web email address? Or do you have outlook installed as well or instead on your computer.
Talk of copying them to your recycle bin is a bit out there and probably why people think you might be taking the mick. That wouldnt be the most suitable...