Thunderbird won't download email messages from Yahoo (formerly Cox) account

How do you have Yahoo set to authenticate? See <Account Settings | (the account in question) | Server Settings>. If Oauth2, you don't use an app password, just use your normal Yahoo password when prompted. You must have Cookies allowed in Thunderbird for this to work. See <Settings | Privacy & Security | Web content | Accept cookies from sites>.

I think Yahoo may still accept the old, less-secure "normal password" method, which does require an app password.

If you have more than one Yahoo account set up in Thunderbird, you may have to make a couple more tweaks. They are described here, but if you need help with that let us know.

https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo

(Malwarebyes may still be a problem, and it is probably IS running in the background)

I tried the above suggestions and switched to OAuth2. That didn't work. I tried just the password option and got an app password. That didn't work either. I checked and it accepts cookies. All I seem to get in regards to progress is showing at the bottom that TB has 240 emails and tries to download one of 240 and the program times out before downloading a single email.

Did it happen exactly on a version change? Coming from which version? (version history at Help > Troubleshooting Information > Show update history?

Yes. There was an update that occurred on 27 Aug 2026 and the email stopped flowing to TB. There have been two updates since. As previously mentioned, Yahoo tech support tried to remotely repair whatever the problem was and worked with me for over 45 minutes on a tech support call.

I just looked at my other setup on a separate laptop and it requires Oauth/2 on the incoming side and a password for outgoing mail. Its working fine. I stripped out and reinstalled the Yahoo app password for the problem account. I'm able to send email on this account using TB but it continues to balk on downloading. In testing the connection, both incoming and outgoing are testing fine in the setup. I've eliminated some of the obvious spam in the web based version of the Yahoo account but things haven't moved at all. I also Malware Bytes to look for any viral issues, none detected.

Whenever I attempt to download, it starts with 1 of 265, or similar, and just stops. Is there something in the downloaded items causing this?  What should I look for?

I stopped receiving/sending emails on 8/28/2026. I have multiple email accounts that were transferred from Cox to Yahoo, My hardware is MacOS silicon. All worked on 8/27/2026 and all accounts have stopped. All have authentication set to OAuth2 and cookies enabled.

I moved Thunderbird to another computer with a functioning set up for Yahoo as well. It had POP3 settings and I accidentally erased the profile. I then reinstalled that profile and it worked without any problems. The profile on my wife's computer was transferred to that same copy of Thunderbird and it still failed. I spent two frustrating hours on tech support with Yahoo and the needle didn't budge. It would start to download messages and fail after no more than 12 messages and always the same 12. I even tried Better Bird as an email program. It had the same problem. I also attempted to use an additional email program and it had issues too. The problem seems to be on Yahoo's end but they can't fix it. I gave up on POP3 for that account and it's downloading again but with IMAP settings. I started this odyssey naively believing that tweaking the security settings or changing the app password would handle the problem. I even archived 300+ emails on the Yahoo webmail page and then tried to download the remaining 1. It choked. Thanks for your suggestion but this turned out to be insurmountable with POP3 settings which have been working fine for several years. It doesn't explain why one Cox email account using POP settings is unimpaired and has the same version of TB.

That all does seem to implicate something funky on the Yahoo side.

It's a bit unclear to me whether you did this or not, but I have seen the situation where a malformed email gums up the queue on the server. Unless it's somehow obvious which one it is, the remedy is, using web mail, to move everything out of the INBOX to a temporary folder, then start moving them back into the Inbox in small batches and initiating a download until the bad message is identified and deleted. It can be a tedious process. This is nothing specific to Thunderbird, I've seen it in other email programs as well.

I don't think that the fact that Cox works and Yahoo doesn't means anything. It has to do either with something wrong with Yahoo or with a particular message in that Inbox.

And I still think it's possible that Malwarebytes is at least part of the problem. They are infamous for it.