Troubleshooting Yahoo Mail Login Errors
After enough years of doing this, I've noticed Yahoo login problems really do sort themselves into a handful of predictable buckets. Working through them in order saves the most time, so that's how I'll lay this out.
"Incorrect password," over and over
First thing I check: is this an old password saved in a browser's autofill, left over from before a change? If you've reset your Yahoo password anywhere recently, that's the only one that works now — every old saved login elsewhere keeps failing until you update it manually.
Account temporarily locked
Yahoo locks accounts after several failed sign-ins in a row as a security measure. It's not the same as being hacked, and retrying the same password just extends the wait. Give it time, or head straight to account recovery instead of guessing again.
A third-party app rejects a password you know is right
If two-step verification is on, apps outside Yahoo's own — Outlook, Thunderbird, your phone's built-in Mail app — need an app password made specifically for them. Your regular Yahoo password simply stops working there, with no warning that this is why.
Sign-in page won't load or keeps redirecting
Try a private browser window first. I've seen ad blockers and privacy extensions interfere with Yahoo's sign-in specifically, even when they behave fine everywhere else.
"Unusual activity detected"
An automated flag, not necessarily proof of a real breach. Follow Yahoo's own recovery flow rather than a link from an email claiming to be from Yahoo — that combination of urgency and a login link is exactly what phishing tries to imitate.