Try changing the hotmail/outlook/live accounts to use oauth2.0 authentication. Microsoft are in the process of some sort of rolling change to force folk away from normal passwords.

Perhaps use the yahoo server they suggest https://help.yahoo.com/kb/imap-server-settings-yahoo-mail-sln4075.html for IMAP.

Based on the two links, yours and mine. I really do not know what language they are speaking in, but confusion appears to reign supreme at Yahoo.

Perhaps the export server is some backhanded way of implementing something like Google takeout. What does appear clear is the export does not sync both ways, based on the statement and link at the bottom of the page, so it is not really an IMAP mail service. I really do not know what it is. I wonder if Yahoo do?

You might want to check in your settings for Thunderbird that cookies are allowed (some third party products disable them). They are required to establish an oauth account token.

You might want to make sure you do not have any application monitoring the localhost adapter. Things like a web server, some application development environments and some security product lock down the localhost which is used in the oauth process to pass the oauth2.0 authorization token to Thunderbird from the web

While the automatic conversion was some time ago, the troubleshooting steps shown are still quite relevant for all oauth2.0 connections. https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20

Hi Mat, thanks for your responses. Before testing your recommendations, I did a couple of things. First I ran sfc /scannow which located and fixed some corrupt files. Second, I checked my Avast Free antivirus(v23.11.6090)and the firewall was off, Windows firewall is on. According to this article https://support.mozilla.org/gl/questions/1375468 "Thunderbird must be an allowed program" through the firewall, and yet it is not in the list for allowed apps., so I added TB to the list. I had previously checked cookies (which is set to accept all cookies), and checked that there were no exceptions. I had also checked the Java setting using the config editor, and it was enabled. I also checked these things in this article https://help.mashme.io/support/solutions/articles/29000036898-how-to-see-if-windows-firewall-is-blocking-a-port-or-program and everything seemed fine. None of the above actions made a difference BTW. In terms of checking local host, I`m not that knowledgeable, and had to look this up. I don`t know how I would set about checking if software is redirecting to local host. I can say that my pc is a personal one, not gaming, not hosting web sites, and I`ve covered the firewall, ports etc already. As for setting both web outlook accounts to OAuth, this is what happens.

If I use the settings from this article https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/pop3-and-imap4/pop3-and-imap4 the incoming mail still works (as it always has). However, if I try to send on either outlook accounts(I`ll call them owl1, and owl2), I get the error

        "Login to server smtp.office365.com with username owl1@outlook.com failed."
                 "Retry    Enter new password        Cancel"

       "Sending of the message failed. 
        Unable to authenticate to outgoing server (SMTP) smtp.office365.com. Please check the password 
        and verify the 'Authentication method' in 'Account Settings|Outgoing server (SMTP)' 

Additionally, despite being two separate outlook accounts, if I change the port number in one account, it changes the other account as well. And, the username in both accounts is the now the same, and If I try to change it, it gets changed in both accounts, so one of my accounts has always got the wrong username. (ie., when editing the smtp settings, under "account settings") I checked the Google article you suggested. The cookies and Java steps I mentioned earlier. I checked the stored passwords. My GMAIL account which has always worked has passwords for IMAP, SMTP and an OAuth token. My owl1 account also has all 3, and the IMAP & SMTP passwords are the same (It is a Microsoft App generated password). My owl2 account only has the OAuth token. BTW, Microsoft sent me a email saying they noticed the login attempts on my owl2 account, and told me to set up using a MS App generated password, which is what I`ve been doing. (and how it was originally set-up).

As for your suggestion to change settings on my Yahoo account according to your link, I had tried these settings previously, and I tried them again with authentication set to OAuth2, and no change.

The errors are

            "Sending of message failed. The message could not be sent because the connection to Outgoing      server (SMTP) smtp.mail.yahoo.com timed out. Try again."

The incoming also has time-out errors. NB. There is also no passwords/tokens stored for this account.

Just to jump in with a comment. I lack Matt's expertise overall, but I did notice something. The fact that you mention changing one account also changes the other indicates you are using the same SMTP server for both accounts. You can verify this by clicking 'account settings', scroll down left side to Outgoing Servers SMTP, and listing the entries. There MUST be one for each account. Edit each with a different description and then check the account pane to see which smtp server it links to. This indicates you are emailing for one account and using a different account for sending, resulting in failure.

Hi Dave, thanks for your response. TBH this problem wasn`t part of the original problems. However, when I checked the "outgoing server (SMTP)" under "Account Settings" there was some irregularity (I think you were right about the same smtp server used on both accounts) So, I selected a different server from the "Outgoing server (SMTP):" drop down box under "Account Settings". Then selected "Edit SMTP server...", and checked the settings especially the username. This is all good. Now, both accounts have their respective usernames, and changes made in one do not affect the other. NB. Bar the username both accounts have exactly the same settings, including the name of the smtp server ie., smtp-mail.outlook.com. However, this does not fix my problem regarding sending email from this account(owl2@ouytlook.com).

Additionally, after changing the first account(owl1@outlook.com) to normal password, I can send mail from this account. The stored password in the manager is the original 'MS generated App password', that I originally used to set up the account. The settings are

"Account Settings" -> owl1@outlook.com -> Server Settings -> Server Type: IMAP Mail Server -> Server Name: outlook.office365.com

                                                                                                                                            Port 993

-> User Name: owl1@outlook.com

                                                                              -> Security Settings -> Connection security:     SSL/TLS

-> Authentication method: OAuth2

"Account Settings" -> Edit SMTP Server -> Settings -> Description: Microsoft -> Server Name: smtp-mail.outlook.com -> Port: 587

-> Security and Authentication -> Connection Security: STARTTLS -> Auth... Method: Normal Password -> User Name: owl1@outlook.com

So, this is the outlook of my primary MS account(owl1@outlook.com). It now both receives and sends mail from within TB. NB. There is no option for OAuth with this server. The second outlook account(owl2@outlook.com) has exactly the same settings as above, except for the user name, AND, the now correct smtp, though it is also smtp-mail.outlook.com. I can receive mail but not send it from this account from within TB. I have tried using a different smtp (smtp.office365.com) which does support OAuth, but cannot get it to send email, no matter what I do. No matter which smtp server I use, whether I use OAuth or Normal Password, whether I use the original MS generated Password, or the newly generated password, It will not send. As for my Yahoo account, it has not changed, ie., it will not send nor receive.

I have no advice to offer, but I will share my settings that work: My yahoo is imap.mail.yahoo.com (993, and smtp.mail.yahoo.com (587, standard, not Oauth2) My outlook is office.outlook365.com (993), and smtp.office365.com (587 starttls, oauth2)

Thanks anyway. I`m guessing you mean outlook.office365.com. I`ve tested all these settings without success. I don`t know whether it`s relevant but, if I use smtp.office365.com there is no option for Oauth.

Cheers, D.