Recent answers to Thunderbird server does not support selected authentication methodhttps://support.mozilla.org/fa/questions/13177592020-12-12T19:50:38-08:00more info here.
for "att.net" based email mail-servers, first get a (secure mail key) SMK code from 2020-12-12T19:50:38-08:00atErikhttps://support.mozilla.org/fa/questions/1317759#answer-1375576<p>more info <a href="https://support.mozilla.org/en-US/questions/1315734#answer-1373022" rel="nofollow">here</a>.
</p><p>for "att<em>.</em>net" based email mail-servers, first get a (secure mail key) SMK code from att web mail access website , use the code as password in the TB's att mail-account (it should use "Normal Password" auth-method &amp; SSL/TLS security as shown in the link) , before adding code as password, you should remove earlier password from "Saved Passwords" in TB , restart TB.
</p><p>above is sufficient, but if you want to use OAuth, then enable Cookie in TB &amp; change authentication method (auth-method) from "Normal Password" into "OAuth2", click on Sent/Inbox, etc folder, and follow the OAuth verification process . restart TB.
</p>Use the correct server settings given here:
https://www.att.com/support/article/dsl-high-speed/KM1012020-12-12T06:22:25-08:00sfhoweshttps://support.mozilla.org/fa/questions/1317759#answer-1375443<p>Use the correct server settings given here:
</p><p><a href="https://www.att.com/support/article/dsl-high-speed/KM1010523/" rel="nofollow">https://www.att.com/support/article/dsl-high-speed/KM1010523/</a>
</p><p>Use 'normal password' authentication but enter a secure mail key instead of the account password:
</p><p><a href="https://www.att.com/support/article/email-support/KM1240308" rel="nofollow">https://www.att.com/support/article/email-support/KM1240308</a>
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