Thunderbird is useless. Every time I restart the computer all my emails and personal folders disappear and gradually start to re-appear hours later. I need a reliable email program that leaves my personal items on my computer.

Is this an IMAP or a POP account?

It's an IMAP account. Thunderbird has uploaded all my folders and thousands of archived old emails to the Talktalk mail server and I seem to be locked out now on my Windows 11 computer, nothing has been downloaded today. I am using the old Windows 10 machine.

Speaking to your original question, the slow appearance of messages is not Thunderbird, but the server. Thunderbird initiates a request for messages and then must wait for the server to respond.

I meant to say that Thunderbird is locked out of the Talktalk mail server. The archived emails were intended to be kept on the Windows 11 computer, not sent to the mail server. Now they have all gone from the computer. This old windows 10 computer still uses Windows Live Mail, which can access the server no problem.

By 'locked out' do you mean the password is not being accepted? Also, if you are accessing the mail from Windows Live Mail, then the messages are on your PC somewhere. Email clients must download messages to read them, which is what thunderbird does.

By 'locked out', while Thunderbird was attempting to download emails from the server I tried to access the server on webmail through Firefox, but there was just a rotating 'wait' symbol and I couldn't log in. I will try the modification suggested by Christ1, thanks.

I have version 159.0, with scads of problems. Is version 160.0 ready for download? If so, has anyone tried it and can they verify that it works? I regret to say that Thunderbird has caused me much grief over the years.

If I may offer a personal observation: the ESR version is more stable, and users are subject to updates less frequently. And there is no need to update just because there is a new release. Many are still using 115, 102, 91, and even earlier. My suggestion is to consider changing your strategy about updating regularly. New features are always welcome, but new features introduce new code, so occasional blips will happen. Just my two cents here... Instead of anticipating 160, another option is reverting to 153.

Thanks, christ1. I followed your directions and it worked. We have been researching our family history for more than 25 years and we have a large archive of emails from distant relatives across the world.. We were worried that it could all disappear! Thanks again.