Top posting, because before you do the below, you should consider this:
There are two ways of using email on Linux.
Your email stays on a remote server (e.g. your ISPs) and Thunderbird looks at it there. (I suspect that's what you're doing). or
You run some sort of daemon/server on your computer, e.g. Exim (but there are others). This fetches the the mail from the remote server and stores it locally. Thunderbird then talks to your local daemon/server.
If you're using the first method, like I suspect you are then: If you're like me and keep most of your emails, over time, you can end up with tons of stuff, particularly if people have sent you emails with large attachments.
There are two main ways of communicating with a mail server to fetch mail, IMAP and POP (POP3). IMAP is quite efficient. I think POP is not quite as efficient, but it may be that, when thunderbird connects to your ISPs mail server, it's having to check every single message. Over time, this could cause things to slow down.
A) If you've noticed a sudden slow-down, then it's more likely that something has broken, or configuration needs to be changed. B) If you've noticed a gradual slow-down, then this might be what's occurring.
If it's B, then the advice used to be, (particularly using POP), delete messages you don't need. Also, Thunderbird has "Local Folders". Basically this is a mail store that sits on your machine. You can move emails from your ISPs mailbox to a Local Folder. This will delete it from your ISP and put it onto your computer where it should be accessible quicker. The drawback of this though is that it's then only accessible on that one computer. Another drawback, is that you're at the mercy of Thunderbird to store the emails. It's good, but I don't do this, except as a backup.
Now, my other thoughts below...
On 21/02/2021 22:54, Bev Nicolson wrote:
Done that (the Lifewire suggestion) and have a novella. What am I looking for? Anyone done this who can interpret them?
OK. I suggest that you do it again. Wait for it to log-in successfully, then shut down Thunderbird.
I just tried it on my system. I got messages D/IMAP and I/IMAP. I'm *GUESSING* that D/IMAP is Thunderbird sending to the remote server, and I/IMAP is it receiving. (Obviously you'll have to set the logging to check the right think - set it for POP3, IMAP or both depending on which is slow. If you don't know which is slow, set it for both.
I'm getting messages like D/IMAP Try to log in
D/IMAP got new password D/IMAP login succeeded
If there are any lines that say error, or timeout or failed, or something similar. I'm guessing that might be the problem.
Good luck.
Steve