Do you have authentication method set to OAuth2? Are you using a third-party antivirus solution?

Hi, thanks. Yes, the authentication method is set to OAuth2. I use McAfee and tried downloading mail with the firewall off which didn't change the problem. I couldn't find anywhere to check a whitelist on McAfee although I've never had a problem with them interacting with Thunderbird before.

It's not just the firewall that affects Thunderbird's normal operation. You should restart Windows in safe mode with networking and test Thunderbird's Yahoo access. You may have to use a wired internet connection because wifi may not work in safe mode with networking. If this is not an option then you should uninstall McAfee from your system, making sure to reboot then test Tbird.

I wasn't quite sure how to do the safe mode approach but I did spend an hour with McAfee support who uninstalled McAfee (during which time I tried to access Yahoo via Thunderbird) and then reinstalled it, with no change - Thunderbird still won't access Yahoo for some reason. The McAfee support tech says it has nothing to do with their antivirus program unfortunately. For what it's worth I downloaded Mailbird as a temporary fix and it can download the Yahoo mail no problem so I don't know what's going on with Thunderbird except that the same problem happened at the same time on two different laptops which aren't synched to my knowledge.

Just an update if there are still any trouble shooters out there. I talked to Yahoo support and they think Thunderbird must have updated something recently that doesn't synch with Yahoo's log in process anymore. I tried app passwords and was able to send a test message out but I still can't download any mail on Thunderbird. I'm guessing there isn't any official support line for Mozilla. So far McAfee and Yahoo say the problem's origins come from Thunderbird.

This forum is not boiling over with frustrated yahoo users. So I don't think it is a Thunderbird change.

My personal opinon of yahoo is nothing they say or do can be trusted. The McAfee folk appear nice, but the product has had issues since 2012 with messing up email. It is like they just don't understand email. Or don't care.

However notwithstanding my opinions. Safe mode with networking is still the best approach as it eliminates all sorts of things, not just the anti virus. To diagnose problems with Thunderbird, try the following. Including Thunderbird troubleshoot mode in windows safe mode with networking: Note a wired internet connection is required. WiFi apparently does not work in Windows safe mode)

• Restart Thunderbird with troubleshoot mode. On the Help menu, click on "Troubleshoot mode" and continue when prompted. If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Please report results.

I don't know what's going on with Thunderbird except that the same problem happened at the same time on two different laptops which aren't synched to my knowledge.

Are the two laptops connected to the same local network and using the same internet connection? What else is common between the two laptops besides Thunderbird? I have a Yahoo account (it's the oldest of my accounts) in Thunderbird and it's working just fine, but not before I turned off the Mail antivirus component of Kaspersky and added yahoo.com (and aol.com) to the list of trusted addresses to exclude it from scanning of encrypted connections. Sometimes a simple uninstallation of security software is not enough to completely get rid of it from your system. Their uninstallers are purposely written to leave stuff behind for quick reinstallation later on. Most products have a standalone "uninstaller" or "remover" utility that is supposed to completely remove a product from your system, but in my experience that is often not the case. They clean up enough for an error-free reinstallation of the same software, while still leaving things behind! A search through the Registry and filesystem quickly finds remnants even after running those cleaners multiple times. The point is, getting rid of AV components from your system can be a murky affair, short of a clean Windows reinstallation. Windows safe mode presents the best troubleshooting instance where third-party software components are under investigation.

Hi Matt and Stans,

Re: safe mode: to my embarrassment I don't have an ethernet cable with a compatible connector to either of my laptops. I'll have to order one - and hopefully find that 48 digit Bitlocker recovery key (this is why I'm willing to pay someone to fix this) - but in the meantime I can tell you that in Thunderbird troubleshoot mode I am able to send messages but not receive them. On the other hand I can also do that in non-trouble shoot mode. The tech support person I initially worked through this at Yahoo (2nd level and seemed to reasonably know what he was doing) had told me that if I could send email but not receive it on Thunderbird even while using the app passwords the problem is not with Yahoo but Thunderbird. I also got the impression from him that not a lot of Yahoo users utilize Thunderbird these days which may be why he isn't getting complaints (but who knows).

My two laptops which are having the same problem with Thunderbird are of different brands but both use Windows 10 and McAfee as well as other software. While normally they both use the same internet connection I experimented by connecting my main laptop to my cell phone hotspot (not the same company as my home internet service) and tried downloading mail with Thunderbird. There was no change. It's conceivable it has something to do with a McAfee update but if so the block only works with Yahoo and not gmx - both of which I access from Thunderbird - nor is there a problem with any other mail program I've tried to download my Yahoo mail. McAfee isn't particularly direct about showing its whitelist so I haven't been able to try something a simple as checking that although I'd assume the McAfee guy who worked with me would have checked at the time.

One thing I have learned while trying other mail programs is how much I prefer Thunderbird so I hope I can eventually find and resolve the problem.

Thanks, Donna

Here's my update once I acquired an ethernet adapter and was able to login using Safe Mode with Networking. I was still unable to download email in Thunderbird. So far nothing I've tried seems to point to other software being the issue but I still can't figure out what would have suddenly changed with my mail program midday May 17 to cause it to go down (well, be able to send but not receive email) on two separate computers. (See my earlier messages.) All the obvious solutions (checking settings, etc.) seem to have been tried.

Let's see how a new Thunderbird profile goes. Create a new profile and launch it, as explained here Profile Manager - Create and remove Thunderbird profiles. Set up your Yahoo account. Do NOT remove your previous profile.

I tried creating a new profile and there was no change - I still couldn't download any email. Earlier I had also experimented with uninstalling and reinstalling Thunderbird on my second computer where I don't keep most of my email folders (so no real risk) and when I reinstalled it apparently my computer had retained all my files and email but in any case nothing changed in terms of being able to download email.

When you launched the new profile, did the OAuth2 window open, prompting you to sign in to your Yahoo account?

Yes, I did have to sign into my Yahoo account. I got in with my regular password but was not sure whether the disposable app password that Yahoo tends to want got attached to this account or not. On the other hand, even in the accounts where I know the disposable password was originally used the functionality was still the same: I could sent mail via Thunderbird but not receive any from Yahoo (although I could receive email from my other webmail). Again, for some reason this problem shows up on both computers that have Thunderbird. All I can think of is that it's related to an update of some kind.

I've been trying to find a pay service that can fix this (I've had a number of dead ends here in that regard). Is there a call line particularly versed in Thunderbird? I'm going to try taking it to a computer repair guy I went to a year or so ago but he's pretty booked up.

My computer guy spent hours trying to figure this one out and concluded that my specific Yahoo account (but not most others) has stopped being able to communicate with Thunderbird. This was the first error message that showed up when the problem started:

yahoo oauth2 fails NS _ERROR _NOT _IMPLEMENTED: Component returned failure code: 0x80004001 (NS _ERROR _NOT _IMPLEMENTED) [ns IRequest .name] OAuth2 .jsm:171

Similar error messages showed up as he tried to troubleshoot. The problem continued on both my computers as well I think as when he tested on one of his laptops using my email account. When he created a new test email account for me in Yahoo it worked just fine with Thunderbird.

If it were anything but my most essential email account I'd just use another one with Thunderbird but as it is I'll have to resort to other (worse) mail programs unless the problem resolves itself eventually with updates. Why, after 14 years of having this email account it suddenly stopped working with Thunderbird the afternoon of May 17, I have no idea.

You could try reverting back to Normal Password authentication method (for both incoming and outgoing) and use a freshly generated app-specific password (not your normal Yahoo password). This should work just fine.

Also, consider changing your Yahoo account security settings (via a browser, not Thunderbird). For example, you could change your password, turn ON 2-factor authentication and save. This may force a "refresh" of your account on Yahoo's end so that it can be accessed via modern authentication methods (such as OAuth2). It's not a common occurrence, but it has happened on at least one very old Gmail account, and if you're lucky, it just may fix things for you as well. If it doesn't, there's always the option of using the app-specific password.

Unfortunately none of these things worked. I finally gave up and created a new Yahoo email account which works just fine with Thunderbird (although I'll have a lot of contact updating to do). After trying other mail clients I realized that if I had to make a choice between giving up using Thunderbird or creating a new Yahoo email account I'd prefer to do the latter. At least all of my folders from the old account are still in Thunderbird and I can access incoming mail for the account elsewhere while also technically being able to send (if not receive) email from the account in Thunderbird. I think for whatever reasons on May 17 my original Yahoo email account and its connection to Thunderbird was the victim of a bug or anomaly of some sort for which there is currently no solution.

Thanks for checking back on my case and for all your troubleshooting suggestions. I appreciate your time.

Belstone