You need to supply more information. What OS are you using? What version of Thunderbird?

Have you just installed Thunderbird for the first time and trying to create a mail account? If yes : Thunderbird might not be able to access the internet - so check your Firewall. Exit Thunderbird. Access Firewall Thunderbird must be listed as an allowed program. So make sure Firewall does have Thunderbird as allowed program.

Are you trying to create a mail account for an email address? The password may be correct but not for the settings you are trying to use. Check the user name is correct - most server want the full email address.

Do you already have mail account and it worked ok, but suddenly it is asking for a password? Do you normally auto save the password so Thunderbird connects without bothering you or do you normally enter it each time and never save it?

Confirm password is good by doing the following: Are you able to logon to the webmail account via a browser using that password? Please test this because if you cannot access webmail with that password then Thunderbird will be able to it either. If you have forgotten password, so cannot access webmail - there will be a 'Forgotten Password' link which you need to use to regain access to your webmail account. Once that is done you can reset the password. Please confirm the password gets you access into webmail account.

Some servers have been changing the authentication required. Some now require 2 step authentication and use of an app generated passcode. Some are offering OAuth2. We can advise if we know what server you are using. What server are you talking about? gmail, aol, yahoo, comcast, etc ? What type of mail account are you using IMAP or POP ?

I've just discovered that you asked this same question 2 days ago and someone tried to help you. But you did not get back to them.

When you get an email letting you know when a comment has been posted - in other words you are reading this now - in that email just below the text will a blue button with the text 'Post a Reply' - click on it. It will auto open a new tab in your browser going direct to this forum question where you can post your responses to questions. Do not attempt to use 'Reply' to the email itself because it is a 'no-reply' email address and it does not work. You have to post comments by using the forum and you do it in the question you have already created.