Are you using a mailkey as required by ATT and yahoo? https://www.att.com/support/article/email-support/KM1240308/

I have multiple accounts that all started going bad last week. One of them I did the long and complicated process of updating, last year, using Authentication Method to use OAuth2 (or what I can't remember?) but I lost the instructions. Is there anyone who has step by step, how to recover my accounts? Old passwords work online, passwords do not work using Thunderbird. (not Thunderbird's fault - Yahoo, ATT, Prodigy and all the rest have changed, without telling us how to repair things)

Does anyone have a simple and straight forward, tested, step by step instruction set to repair this?

PLEASE?

Where is Yahoo support on this?

I was writing while Matt was answering. Going to mark that link and try to go fix things. :-)

I gave you a link to ATT's instructions. If they are inadequate, I suggest you contact them and ask them to explain it to you as you are their paying customer.

If you want support from Yahoo, I suggest you ask them for it. They will certainly not be monitoring this forum looking for customers.

I generated a AT& Secure Mail Key which was all letters. I tried to change my password to the Mail Key, but ATT/Yahoo Mails requires 1 number in the password. So it would not take the Mail Key. I called AT&T they told me to add a number to the key, I did, it changed the password. But again Thunderbird would not accept the Yahoo Mail Key password. AT&T cannot give me an answer. I tried to sign up for Yahoo Paid Support but when the app asked for my Yahoo Email address which endes in @att.net, Yahoo responded they do not support this type of customer.

I appreciate the good link Matt, I wrote my first reply at the same time as you were typing the link. +++

I recovered a couple of accounts and made notes. The idea is, yes the AT&T instructions are interesting and useful but don't include the details on how to do this in Thunderbird. So here's my version for anyone trying to grind through and get their email back. BTW my phone has no issues, gets mail just fine. (so far) I have an assortment of laptops and desktops, some are old and I keep going, only for SCSI cards or software that works on WIN 98SE. Best of this is, I'm taking all email off those computers as it's just a burden and unnecessary.

This is for a Prodigy account (remember Prodigy anyone?) AT&T login

Go to the AT&T login > Login > Profile > Manage Secure Email Key Nice, it creates a key which people will want to not only copy but save to a file for the future. I did that and I always had a notebook for all email passwords. Note your online password doesn't change, just your secure email password?

Thunderbird: Tools > Options > Saved Passwords Delete the saved password for the account Paste the new Secure Password Get mail, which should work now Send a test email > Paste the new Secure Email Password, or you will have to do that some other day.

Everything should work just like it did before. You can receive and send email with Thunderbird.