You need to change the authentication method to OAuth. That is all, unless other parts of your account settings are not up to date.

Thank you for the suggestion, but it is not so simple. I have changed my Outlook accounts to 2step verification. That indeed brings up a OAuth2 authentication method in the Thunderbird profiles. However, when I try to access those accounts in Thunderbird, Microsoft sends back a message ordering me to create an app password and to apply it. Outlook rejects the password. I can still access all the Outlook accounts in Outlook, but Thunderbird is dead in the water. I realize that this is a Microsoft problem, but have you tried to implement OAuth2 with success? How did you apply the app password? The Thunderbird mail client is vastly superior to the Outlook mail service, but after Sept 16, it will no longer be available with normal password authentication. Suggestions?

re : I have changed my Outlook accounts to 2step verification.

If you have set up 2 step verification then you have to use an app specific password. This means you cannot use Oauth because Microsoft are not expecting a normal password to set up OAuth token. Account must use Authentication Method = Normal Password for both incoming and outgoing smtp

• In Settings > Privacy & Security
• click on 'Saved Passwords
• click on 'Show Password'

• Edit the Password for both 'Mailbox:// (if pop) or imap:// (if imap) and also smtp://
• Right click on line and select 'Edit Password'
• completely clear all content and then enter the 'app specific password'
• Do this for both incoming and outgoing.
• Click on 'Close'
• Restart Thunderbird.

IF you want to use 'Authentication Method = OAuth' for incoming and outgoing in Account SEttings' You must switch off the 2 step verification via webmail which also means you do not use an app specific password.

In Thunderbird

• In Settings > Privacy & Security
• Under 'WEb Content'
• Select to allow 'Accept cookies from sites'
• Select to allow third party cookies - always'
• Click on 'Exceptions and make sure to allow anything from outlook.com, hotmail.com, live.com, microsoft.com

• click on 'Saved Passwords
• click on 'Show Password'
• Remove all lines that store current password for that account both incoming and outgoing.

• Exit Thunderbird

Make sure no VPN is running. Make sure nothing is using the localhost such as 'Apache' - some people may use this if they create/maintain websites.

Start Thunderbird You will get a prompt from Microsoft in a browser looking window Enter normal password and clickon Next then you get a second window where you have to allow Thunderbird access to server - click on 'Accept'

An oauth token then gets saved in the Saved Passwords - line start oauth://... From then onwards Thunderbird uses the oauth token to access server.