This happens to me too.
[IMAP] Cannot open folder “/Inbox”. (NO [AUTHENTICATIONFAILED] SELECT Invalid credentials)
Oddly, it continues to sync messages just fine, though not always fast sometimes.
I found an article at Yahoo:
It says “If you receive an error message like “Server password has changed” or “Authentication failed,” your app might be outdated. The app likely has outdated security protocols and are disabled by default.”
So according to Yahoo eM is using outdated protocols, rather than Yahoo servers having outdated software or something.
If I follow further, go here:
It says: “If you try to use Yahoo Mail in a third-party email client using less secure sign-in technology, you might get a “Server password has changed” or an “Authentication failed” error message. This is because those email apps use outdated security protocols and we’ve disabled access to them by default now.”
Well, we do get “Authentication failed” messages, so again eM must be using outdated security protocols.
It also says if people have an account key or use two-step, this can be an issue and might be the cause for some people. For me personally, I don’t have those turned on, it’s just my user/pass is all.
Before eM makes the random claim Yahoo’s servers are bad/old/outdated as if they had like one server somewhere on GoDaddy they forgot to update. They have a massive infrastructure like anybody else. They have 225 million users sending/receiving 26 billion messages a day. It’s not likely Bob the IT guy forgot to run apt-upgrade.
I don’t know who is ultimately at fault. Yahoo can connect with the oauth stuff, or an app password, but it doesn’t seem likely it’s their server being out of date. As others have mentioned, there are plenty of other email apps that connect to Yahoo fine while eM doesn’t.
I’m not here to blame because I have not clue which is at fault, but I’m going to guess 225 million people using Yahoo every day from all sorts of clients are doing just fine.
I would at least suggest eM try their darndest to figure out if there is something up with protocols or SSL or encryption keys or storage of data or character encoding or any possible way to make the connection can be a little more robust.
I know it’s easy to say “the server sent an error, so it’s there fault.” Ya, the error is that authentication failed, so why is the authentication failing that eM is trying to send/use?
If I try to log in to Gmail and type the wrong password and it says “authentication failed” I don’t just say “well Gmail’s servers are sending errors, must be their fault”.
Yahoo is only about 7 years older than Gmail, and Gmail itself is practically “ancient” from 2004. So just saying a service is old doesn’t mean anything. They clearly use 2FA and oauth like everybody else.
All I ask is spend a bit more time being absolutely positive, because other email clients continue to work fine while eM doesn’t. Even if it’s just a server error, it’s not like some code bug or accident, there is a reason for the error, something wrong in the communication standards or something. Hopefully eM can work around it, even use “older” protocols or techniques if that’s what it takes.
Anyway, since the email continues to sync, the error hardly makes sense, so I disabled the error popups out of convenience.