I have a very similar problem to the one described by james blouie. I have an sbcglobal email account that has been working great with TB for many years. Suddenly on 11/12 I did not receive email after 4:25pm PST. When I tried to get email, my request would timeout and I would get an error message from TB that TB could not connect due to a server error.

My original config was POP3 with inbound.att.net / port 995 / TLS/SSL and SMTP outbound.att.net / port 465 / TLS/SSL. This matches exactly to the AT&T recommended values and had worked for many years. I deleted the account and then created a new account with the same POP3 settings. No luck. Then I tried using IMAP and the AT&T recommended settings. It still would not work. As recommended earlier in this item, I also changed via TB Options the minimum level of TLS from "3" to "1". That did not help.

Even though the initial test works during account set-up when I press "Done" TB keeps telling me there is an error with my userid, password, or configuration. I have cut & pasted these values multiple times, including the full email ID, to help prevent typos.

I am able to access my sbcglobal email from other devices. This seems to point to a change to TB on 11/12 that caused the problem. What changed on 11/12? Thank you.

....Image of POP3 Inbound config provided with the front part of my ID removed....

I have the same issue as jamesblouie, it has not been able to connect to my ATT yahoo mail since 11/4/20. Worked perfectly prior to then.

jamesblouie and mlochiel This question was all about the server not using up to date TLS and so the minimum TLS had to be altered in Thunderbird preferences. This was indicated as the solution - see 'Chosen Solution'.

This is not the same issue with ATT Yahoo, so the 'Chosen solution' will not be of any use to you. So you should have started your own question. However, AT&T and Yahoo have changed how they allow connection to server. Create an ATT Secure Mail Key and used it in place of the ATT account password. See info at the ATT support at the following link: https://www.att.com/support/article/email-support/KM1240308

Got it working by using inbound.att.net port 995

connection security SSL/TLS authentication method OAuth2

created a key in TB did not enable encryption by default

used the key as the PW when prompted by PW manager and it stored them for me under both inbound and outbound.

working fine again!

My Thunderbird stopped connecting today, after it applied an update yesterday (78.5.0). No longer could I connect to 1&1.com, peoplepc.com, and gmail.com, nor any of the emails I have on those servers, no matter my personal domains. I tried the solution to change security.tls.version.min from 3 to 1. This did not fix the problem.

I called 1&1 since I pay for my domains there, thinking maybe my settings were out of date, if they updated to the current TLS/SSL. Of course, their answer was that the problem was with TBird.

Anyway, I tried changing the port to 110 and Connection Security to None. That fixed the problem with all of my accounts through 1&1; however, nothing I do will fix my connection to gmail - the connection keeps timing out.

Any help there? Anyone else having problems with gmail?

I have the same problem, only with att.net on Yahoo. It stopped working on the same day, 11/30/20. Very frustrating because it had stopped working on 11/17/20 and I got it working then by adding a secure key. Now I have no idea how to proceed, none of the suggestions above have helped. Current Thunderbird is version 78.5.

I experienced the same today (12/01/20). Until now every account worked properly but suddenly stopped. The same problem is on my other PC with Thunderbird 78.5.0 I changed Connection security to None (Port 110), and all of my accounts are working again but gmail connections are not. Connection timing out. Changing security.tls.version.min to 1 didn't help.

Same problem with att.net. Changing to Port 110 and None also causes connection to time out

I also tried the security settings changes to no avail, we found a workaround, but it is not pretty. Copy your data to another directory first. Uninstall thunderbird completely. Install and configure from scratch. Test it, should work now. This was successful in every pc that experienced problem. Our smtp was working, but pop3 did not on port 995 with ssl/tls. During our testing we found pop3 port 110 worked with no security, but not a good option.

Please stop posting comments in this question. You are spamming the person who originally posted the question.

The 'Chosen Solution' in this question related to the server not using up to date TLS protocol. If it was a TLS issue then you may have noticed a problem when updating from version 68* to 78*. It would not be same problem if you were already using 78*.

So if setting server to be the same as 'Chosen Solution' worked then reset to correct settings and then adjust the preferences editor security.tls.version.min from 3 to 1 OR just try resetting the TLS minimum and restart Thunderbird. That information was posted in an earlier comment and information is here:

• https://support.mozilla.org/en-US/kb/thunderbird-78-faq#w_after-upgrading-to-thunderbird-78-i-cannot-receive-or-send-email-messages

All servers have different requirements. Yahoo and Gmail server are all up to date so do not have TLS issue. It's not possible to cover everything in one question and if your issue is not a TLS protocol issue then stop posting comments.

Yahoo servers (so that includes eg: AT&T) have changed Authentication Method to OAuth. See information:

• https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo#w_important-changes-to-authentication-method-notice

AS of december 2020 please check if the following applies to you. If you are using ESET/NOD32 security/AV then probability is very high it is causing your problems. According to their forums, you should temporarily disable SSL until they solve the problem per https://support.eset.com/en/kb3126-disable-ssl-filtering-in-eset-windows-products?ref=esf - the problem is being reported by dozens of users https://forum.eset.com/topic/26517-problems-with-thunderbird-and-imaps/ https://forum.eset.com/discover/

Please create your own new question to get Help from the Support Forum.

Here is the solution if you are using Eset Internet Security and can not download your emails after 30/11/2020: 1. Open Eset Internet Security – F5 – Web and e-mail – click on the SSL/TLS row – turn off the Enable SSL/TLS protocol filtering – OK – YES 2. Open Eset Internet Security – F5 – Web and e-mail – click on the SSL/TLS row – turn on the Enable SSL/TLS protocol filtering – OK – YES

Thunderbird account settings Port: 995 (for POP3) Connection security: SSL/TLS Authentication method: Normal password

security.tls.version.min = 3 (default, no need to change it to 1 for Gmail account or any other reliable ISP)

With this settings my Gmail and any other accounts work again properly.

see this page, has info on AT&T-Yahoo, & also some info on other ISP/MSP, etc,etc.

and got a message stating that telnet was not recognized. Paul

Telnet is not enabled by default. See https://social.technet.microsoft.com/wiki/contents/articles/38433.windows-10-enabling-telnet-client.aspx

This topic is now locked because the reporter's issue is resolved.

If you are someone who is still experiencing a problem please see https://support.mozilla.org/en-US/kb/cannot-receive-messages and if that doesn't resolve then please create your own new topic.

Thanks