No relation to Thunderbird at all, just a coincidence. Yesterday, I signed up for a new Yahoo account, to be used as backup for a client's business account thanks to Yahoo's massive 1TB storage. The idea was to add the business account to this Yahoo account as an additional mailbox. The webmail client wouldn't let me add the "other" account and instead, required me to do so via the android app. The process was going well until the password input stage. It wouldn't get past that stage, claiming either incorrect credentials or settings, but upon quiting the app and reopening it, the other account was listed with a red triangle with an exclamation mark, on webmail and the app as well. On the app, it would say the connection had expired and required "reauthorization", prompting for the password it never seems to accept. On webmail, the added account is marked as unverified. Eventually, I signed up for a Gmail account instead and connected the business account in one go and the import started right away. Gmail is using POP for the import and severing the connection with the account won't delete the imported messages, unlike Yahoo's case. I deleted the Yahoo account. Note that I did not add the new Yahoo account to Thunderbird, but still had the same issue you're having. The only difference is that you had successfully linked the account prior while I was trying to link it for the first time with no success. Coincidence? I highly doubt it. I don't see the connection between Thunderbird and the webmail linked account.

Hmm, interesting. Thanks. Maybe I'll uninstall Thunderbird and see if it still does it... But that's 2 days of no notifications for new emails (which is why I use TB at all) just to find out...

Hmm, interesting. Thanks. Maybe I'll uninstall Thunderbird and see if it still does it... But that's 2 days of no notifications for new emails (which is why I use TB at all) just to find out...

Uninstalling/reinstalling Thunderbird won't change anything, because it does not affect your Thunderbird profile. Your Tbird profile is what contains your accounts, messages, settings. See Profiles - Where Thunderbird stores your messages and other user data for details.

If you are convinced that Thunderbird is indeed causing this, then testing is as easy as Quiting Thunderbird. No uninstall necessary. With Thunderbird not running, and NOT connecting to your Yahoo account, the problem should not occur.

It seems to happen late at night at the same sort of time, so I'll leave if off later and see if it still does it. Maybe unlinking and relinking the Yahoo account in the web client set off this stupid bug. I didn't think that it would be Yahoo that's caused it because I've had them linked for years and this warning only started when setting up TB, but I see now it could be Yahoo causing it.

Ah, it just did it in the daytime... With TB open. I'll close TB now and just wait to see if it does it again.

"This mailbox is not syncing with Yahoo and needs permission to resume. This can happen if a security setting or password was changed. Sign in to Yahoo"

No security setting or password was changed - Yahoo is just being annoying.

Well, Thunderbird does not even try to change your Yahoo account settings, more so Security settings. Also, Thunderbird uses OAuth2 to authenticate with Yahoo servers by default, not a password, or your Yahoo password, UNLESS you deliberately and manually change account settings (in Thunderbird) to use Normal Password authentication together with an app-specific password, also deliberately generated from your Yahoo account's Security settings page.

I have no knowledge of Yahoo's server-side workings, but I'm pretty sure that the connection between your two linked accounts is not even happening via the webmail interface. It's all happening in the backend, while the webmail interface is just a visual presentation of what's going on and a means for you to have some control (such as authorizing the link). In addition, the protocols used by Thunderbird to interract with Yahoo servers are not necessarily the same as those used by the webmail client to interract with your account.

It is probable, however, that a server-side limit may have been implemented, that limits how many connections can be made to your account (primary or secondary), and Thunderbird definitely adds to the number of connections made to the account. Since monetizing the service is a high priority, it's not hard to imagine such a thing could be going on. Microsoft did it with their Outlook Mail service. They completely removed the option to connect to another account. AOL doesn't have such a thing as well, and it could be a move to make it a business, paid-for feature in Yahoo. They are just not being obvious about it. This is just speculative thinking on my side though. Thunderbird may or may not be part of the problem. Fortunately, eliminating Thunderbird as the culprit is easy to do.

Yeah it's easy to give up on TB if it is causing it, but I need something that will give me audible alerts when I get a new message. Yahoo's inbuilt alerts are broken.

Ah OK, it just did it again with TB off, so it is Yahoo... Now I need to figure out how to keep the web client and TB open at the same time without it doing that, by unlinking the accounts, or just use TB, or just get used to having to keep putting the PW in...

I just found a way to contact Yahoo, I looked before and thought it was impossible, but they are on facebook. Hopefully they will sort it out.

Thanks for the help.

I would just use Thunderbird and have both accounts added. It's the whole point of using a mail aggregator/collector like Thunderbird anyway, so that you can access mail in multiple accounts from one place. It's odd that you only use Thunderbird for the audible alerts then go back to webmail to read the emails. What's up with that? I understand person preference, but I'm still curious.

I use both to read, but everything just looks better on the web client. And I'm just totally used to it as well, it feels a lot nicer and easier to use, I know where everything is, and how to do things, like send from and make disposable addresses. Just had a quick look and can't find those functions in TB. Maybe I will get used to TB and it'll be fine.