your password on the server changed. hence Thunderbird will need a new password.

I am guessing based on the limited information that you provided that you have enabled two factor authentication and you now get a pin as a text message, in addition to the other things.

In that case you will need to create an application password for Thunderbird to use. See https://support.microsoft.com/en-au/help/12409/microsoft-account-app-passwords-and-two-step-verification

Hi Matt, this is all rather confusing. I have had the same password to log into Microsoft for years and then I was forced to change it to a PIN code. So essentially there is the password and PIN linked to Microsoft. After doing that Thunderbird also forced me to login when I never have to do that since initially setting up the account many years ago. It is at that point I lost all my folders. I thought it a coincidence that both Microsoft and Thunderbird asked I change passwords at the same time. And never understood any link between the two. Regarding your suggestion, the link you sent has so many options to choose from regarding setting up application passwords and there is nothing in reference to Thunderbird. Hence the confusion. I am at a loss and I desperately need my folders and emails as I do a lot of business and community work. A detail list of what I need to do would be really helpful. Thanks in advance. Diana

I'm confused too. I assumed "Microsoft" referred to Outlook or some other MS email provider. However, when you say you are surprised by any relationship of Thunderbird to "Microsoft", I think maybe you are talking about some other product or service from MS? This combined with the fact that all your emails disappeared makes me wonder if you are sure you're logging into the same server and account that you used to log into. (Just shooting in the dark here.)

I was forced to update the login at the 'Microsoft Account Password' point to login in to my computer. For some reason Mozilla/Thunderbird also made me login to get access to my emails which I have never had to do before. I don't use Outlook at all. I have only used Mozilla/Thunderbird for my emails and I set up folders to save emails in an orderly manner. It is those folders and older emails that have gone missing. I hope this explains my predicament.

I've only used local accounts with Windows so I may be way out of my depth here. Who is your email provider? Thunderbird being the client but what server? (Or if that's confusing, what is to the right of the "@" in your email address?)