I'm a user from Yahoo! from a long time ago already... something between 12 to 15 years.
For the most of the time, I can tell you I was a happy user... Yahoo! web interface was modern and I used it too with POP3 (later moved to IMAP of course) and SMTP with different e-mail clients.
From the last few years, well... we all know things are not good with Yahoo! anymore... Google took from it a good amount of the payed advertisement with it's (much more powerful) search engine. But from the past few months, the e-mail system is becoming a pain in the ass.
First, the SPAM filter doesn't work well. And I can't disabled it. I tried to refine it with some training but it seems it will be forever stupid because it keeps putting e-mails from mailing list that I'm subscribed for years in the SPAM folder.
Second, Yahoo! thinks my e-mail client is not secure anymore. Now and then, when I got check my e-mail on Thunderbird, I got a error message stating that the authentication process failed and asks me to try a different password. There is no password change, it is Yahoo! pestering me to stop using a e-mail client (yes, I tested with Claws too).
I didn't change my password, so let's go back to the web interface and see what is going on.
OK, it asks me my same old user and password. And this "nice" Captcha. And here is the reason for not being able to use Thunderbird:
For non Brazilian Portuguese speakers, it says:
"Alceu... disable the less secure access to your Inbox"
Well... that's just bullshit. I use the same authentication method (Yahoo! doesn't asks me for a Captcha unless I got blocked first on my e-mail client) with Thunderbird, and also the connection uses TLS the same way that my browser uses.
Let's also add that I access it from my home network, that is behind a router/firewall, using a cabled connection (not WiFi) and that my PC uses a firewall as well.
What is considered secure as well? Their mobile application... that I should install on a Android, which I have little to no control (unless I got root on it) of how it works and the software that is installed and have to use WiFi or the shitty 4G available on Brazil.
Yeah, it doesn't look very secure too me so... STOP PESTERING ME Yahoo !