What are your server settings? See https://www.att.com/support/article/dsl-high-speed/KM1010523/

Are you using a secure mail key?

https://support.mozilla.org/en-US/questions/1316825

https://support.mozilla.org/en-US/questions/1314254

https://support.mozilla.org/en-US/questions/1312886

What is your antivirus?

POP3 Inbound.att.net Outbound.att.net Logon using clear text

Outgoing 465 Incoming 995

AntiVirus: Malware Bytes

imap.mail.att.net tried both 993 and 995 SSL/TLS Tried both Normal and Encrypted password

Do you have the same account as POP and IMAP, or are these separate accounts?

IMAP accounts with SSL/TLS security use port 993, and authentication for AT&T is normal password. But the password has to be a 'secure mail key'.

I tried both. I've messed with these settings in every logical combination I can think of. None of it worked.

It all worked fine until about 3 weeks ago. Nothing I did changed. Now none of it works.

> It all worked fine until about 3 weeks ago.

So your problem greatly predates your initial posting here on 12/9?

Can you put a specific or approx date on it? Dec 1, Nov 30, ...?

And what recent dates and versions do you see in help > troubleshooting > show update history?

Nov 16 is the latest email on my system. I spent about a week and a half trying to figure this out myself, and another few days getting help from a friend who knows a bit more than I do.

We couldn't solve it. I have the last version of WLM, and ThunderBird78.5.1 64bit

you may also see these various related answers posted here.

Thank you. I have gone through these settings. No joy.

Seems that all this trouble is in the name of internet security, but if so, they did a piss-poor job of implementing it. My email is so secure they made it nearly impossible to access. Strange that so many people would get cut off without any warning, and without the correct information for updating settings. It's not like it would have been difficult to put together something...

please go thru each settings , steps again . please do not hurry , be patient.

apply what is needed for your case from PART-1 (settings, dual account) , PART-2 (settings) , PART-3 (Ant-Virus,etc) , PART-4 (anti-virus software, TB settings for anti-virus, etc).

General instructions again , please patiently go thru this again:

malwarebytes , your AV may be creating a proxy/gateway client-server by intercepting mail-server communication , that needs to be disabled.

imap protocol only uses secured port 993 (and non-encrypted/non-secured 143) . do not ever use 143 or clear password. Do not use "None"-"security", unless for test , but later you must change password , as password gets exposed after using "None"-"security".

in POP based mail-account in TB , use secured POP protocol port 995 , & you must select "SSL/TLS" security , do not use "None"-"security" , & use "Normal Password" as auth-method (authenticaiton-method).

you must select SSL/TLS "security" for incoming POP or IMAP. select SSL/TLSsecurity for outgoing/SMTP.

if you use POP protocol based POP mail-server in incoing , then you MUST not use imap protocol based IMAP server in incoming, in same mail-account.

in POP mail-account in TB, all mail-servers must be POP protocol based servers. in IMAP mail-account in TB, all mail-servers must be IMAP protocol based servers.

but it appears you are mixing two types of mail-servers, or tried after mixing them . that will not work. in TB, if a mail-account was created for POP protocol , then you cannot use IMAP servers/settings in it. in TB, if a mail-account was created for IMAP protocol , then you cannot use POP servers/settings in it. how you can use same EMAIL account via both IMAP & POP protocols in same TB with a trick, is shown here.

at&t uses two sets of servers: one set is for imap : imap+smtp. another set is for pop : pop+smtp. use pop mail-servers in POP based account in TB. use imap mail-servers in IMAP based account in TB. you cannot change a POP based mail-account in TB into an IMAP based mail-account in TB. you have to create new (IMAP) account in TB separately.

And for Windows-Live-Mail please see this answer on MS (microsoft) settings here is useful or not.

PLEASE CHECK THIS AT&T FORUM/COMMUNITY SUPPORT PAGE ON SBCGLOBAL.NET EMAIL HOLDER CUSTOMER. WHAT IS YOUR ISP DIVISION/BRANCH's CURRENT EXACT NAME ? (please look into Billing Statements)

• if current instruction for your email account is to use OAuth , then in TB's mail-account choose "OAuth2" authentication method (auth-method) & SSL/TLS security , & enable Cookie in TB.
• if current instruction for your email account is to use Secure Mail Key (SMK) , then in TB's mail-account choose "Normal Password" auth-method & SSL/TLS security , & generate a SMK code in AT&T's web mail access website & use that code in TB's mail-account's password field/box.

The reason it looks like I'm using 2 different settings is that I'm using 2 different computers, which use different programs. WLM uses one group of settings, TB uses different settings. The account was using POP3 before it went bananas.

OK, here's what I've done in the last 2 days. I've gone through the steps again. I've gone so far as to completely uninstall TB and WLM, and then reinstall them. I have created new accounts and created the settings from scratch. I have tried completely disabling Malwarebytes and Windows Defender. (I've since turned them back on).

Nothing has worked. I've even shared my email address and password with a very, very, very trusted friend to see if he can get it to work on his computer. Neither of us enjoyed any success.

Oh, the Allcaps link to ATT support gave me a blank page. (Never mind--after 3 refreshes it finally kicked in)

It feels like I keep getting told to do the same thing over and over and over again. And as expected when repeating the exact same process, I get the exact same result. --I'd have to be insane (or working with a computer) to expect otherwise, no?

adding below info , if i have forgot to say this earlier: before entering/using SMK , older password must be deleted first from TB. goto Security > Passwords > Saved Passwords > find your mail-account > select mail-account > "Remove". then a restart of TB is needed, for better functionality.

So... Still nothing.

have you gone to the link posted way back and generated a secure mail key to use as your password? I see you talk a lot about settings, but I see nothing about actually creating and using a secure mail key which is essential for SBCGLobal

Since when is it necessary for sbcglobal to create a random password? Rather than one someone might actually remember. Let me guess: since mid-November? Why can I sign into my email via a browser using my regular password? Where's the logic in that. Not your fault, but gotta ask the question.

OK, That got Windows Live Mail working. TB is being a bit of a pain--where did they hide "change password" (sigh) Ended up deleting account and creating a new one.

So, now I can receive email, but I can't send it.

Seriously... WTF?

Seriously. Ask ATT they are your provider and it is their connection and password rules that have to be complied with. They decided to go with a mail provider in Yahoo instead of offering their own service (I assume it is cheap. From where I sit it is certainly nasty.) Interestingly Yahoo owned by Verizon. So despite them supposedly being competitors they are not in email obviously. But then perhaps Yahoo are giving ATT exactly what they contracted to, not what ATT thought they were getting.

My understanding is Yahoo require either oAuth as an authentication method or a mailkey (it is their invention) ATT never actually got their act together and obtained an oAth "secret" that can be used with oAth so ATT customers (You) are left with only mailkey. you could change the server settings to yahoo ones and use your sbcglobal username and password and it would probably work for you to use oAth. but that is really trying to side step the issues.

Have you actually changed the outgoing password to a "mailkey". SMTP and POP and IMAP all have separate passwords in the password store. But if the failure is password, then you get a prompt to put in your new password (mailkey) and an option to save it.

Passwords can be found by going into the options and typing password into the search box. and clicking the saved passwords button when it appears.