First, you can control updates at tools>preferences>general under topic UPDATES. The problems you describe are generally the result of anti-virus software intervening during software updates. I have used TB for almost two decades with never an update problem. If you are using an anti-viruse product, I suggest you see if there is an option to tell it to ignore the email client.

Thank you for chiming in.

What would the antivirus program do to the update, cause it to be corrupted? If so, wouldn't it malfunction in more obvious ways besides giving me error prompts? Besides, TB has been updated many times before without a problem. (Remember, I've had the new computer for half a year -- in that time there would be a lot of TB updates).

I'm not even sure I know how to tell the virus software (which comes standard with Windows 10) how to ignore TB updates. And besides, don't you mean the firewall?

My comment on antivirus was generic; that is, most problems that appear here are caused by interruptions to software updates. However, like you, I use the default windows antivirus and that has never intervened. I have sometimes seen a reinstall fixes problems. For myself, I make backups daily of TB and profile and that has proved useful.

So, you don't know what's going on. Thank you.

Is it easy to downgrade to a lower version before this started happening, or do the developers make it hard to do that? (No lectures on security, please. I've never gotten a virus from an email, even when I used Eudora for ten years after they discontinued it.)

Check that you have the correct settings for gmail: imap.gmail.com on 993 or pop.gmail.com on 995, smtp.gmail.com on 465; SSL/TLS, OAuth2 authentication, User Name = email address. Cookies must be accepted in TB Preferences for OAuth2.

If there are other accounts not working, post the settings so we can examine them.

Disabling TB updates and update notifications is possible, but somewhat complex, and not generally recommended unless you have a critical add-on that hasn't been updated. The best way to install major updates is to install to a separate folder and run in a separate profile, while keeping the previous setup untouched. A bit more involved, but almost guaranteed to avoid update issues.

TB and antivirus apps update frequently, and occasionally there is an incompatibility, but these shouldn't cause breakdowns if you follow the standard recommendation to add the TB profile folder as an exclusion in AV settings, even if it's Windows Security.

sfhowes, some of the things you said I don't understand. Although I was once a troubleshooter in the world of DOS, I didn't keep my technical knowledge up in Windows.

As I said, I spent three hours with my technically minded brother trouble-shooting TB last night, and we couldn't figure out what was wrong. We did discover that if I made Gmail (on the web) my main email client, I could download my emails there, but I don't like the Gmail interface.

In Gmail, we learned that if I changed the user name for each account from aaaaa@bbbbb.com to aaaaa (i.e., removed everything after the @ symbol), I could download stuff normally, but that isn't working in TB.

The problem started less than a week ago. It seems to me that if I reinstall whatever TB release was in effect about a week ago that it might start working again. At one point a couple days ago, I updated TB from 91.4.1 to 91.6.1, and that didn't fix it. (Meaning that I'm still having the problem described in my initial post.)

What release was in effect about one week ago? I think if I return to that, it will start working again.

I'll check out some of the things you said in your comment now.

Thank you.

==

Well, it appears that 91.4.1 was installed in December, so that version SHOULD work, but the program stopped working properly while I was using it, so it wasn't an update that caused the problem.

Woops, this thread is now malfunctioning. My latest comment isn't showing.

Everything I said in my first post is still happening. Changing the format of the user name for each account worked in Gmail but not in TB.

It turns out that a recent TB update wasn't what caused the problem, since the last update was in December, and the malfunctions began about a week ago.

Who is the ISP email account provided by?

The error you mention of an internal server error makes me think that the account you are connecting to simply does not exist on the server you are specifying, or has been disabled by the provider.

So lets go back to the basics here. What mail provider are you actually using? (I am not aware of gmail being offered by any ISPs. Yet Gmail is mentioned here repeatedly, along with server settings.)

Is your account supplied by Yahoo via your ISP? Some biggies in that boat are ATT, Verizon, AOL and some UK providers like some BT customers and I think some Virgin

There's a good chance that the problem is at the ISP. It is a small ISP serving part of Rhode Island. They are not very modern, and their technical people are not sophisticated. The problem is that they refuse to do any trouble-shooting of their email system just because a mail client like TB is not working. They will only trouble-shoot web mail. If I call them up and harangue them about this, they might just hang up on me.

Where I live I have a choice between my current ISP and Cox, and I despise Cox. Cox was raising my price every six months.

Yes, all the accounts that are not working are actual accounts that exist.

What I was saying about Gmail was this: The emails that I can't retrieve with TB CAN be retrieved with Gmail if Gmail is programmed to receive them. Yahoo is not involved.

The solution may be for me to stop using the email accounts associated with my ISP, and to use only the accounts associated with my hosting company.

I will try again. Who is the mail provider? I know you think it might be private but it essential to actually doing more than offering best guesses that may not even be vaguely relevant like I did in the last posting. As you say they probably have an issue and I might even be able to guess what it is. But I would rather run some external test on their servers and see if I get the result I think I will.

Woops. A comment of mine here on the forum just disappeared. I don't think this forum software is working properly.

It has happened three times now: Every time I try to update a comment that I make, the comment is deleted.

Here it is again:

They were a family-owned business called Full Channel in the "East Bay" of Rhode Island (the counties of Newport and Bristol on the east side of Narragansett Bay). A few years ago, Full Channel was purchased by i3 Broadband in Illinois, but the customers of Full Channel still use the Full Channel name. Thus, my email addresses have the format xxxxx@fullchannel.net.

Yes, I'm beginning to think that Full Channel is at fault. If I call them up and say that to them, they are likely to ignore me. Probably the best way to phrase it is to say, "I know my mail program is set up correctly, so there must be something wrong with your system." Calling i3 Broadband in Illinois doesn't do much good because they are giving the original owners free reign to run things the way they always have.

Did you find out anything about my ISP?

yes, I learned that all my guesses were wrong.

So that leaves;

1. Thunderbird troubleshoot mode (it is on the help menu.
2. Operating system safe mode with networking (Instructions on that here https://www.businessinsider.com.au/windows-10-safe-mode?r=US&IR=T>
3. logging instructions on that here https://wiki.mozilla.org/MailNews:Logging

I suggest you try them in that order as the difficulty increases significantly with logging.