I am sure your email provider has a way to reset a forgotten password. But Thunderbird is NOT your email provider and has nothing to do with administering your email password. Thunderbird is email client software running on your computer. You need to work with your email provider to reset your password. Most providers have a link to do this on their email help page.

Having incorrect server settings will also cause the password error message. If you still receive this error after resetting the password to something you can remember you need to confirm that you are using the settings that your provider requires.

Usually, the password used to access webmail account via a browser, is the same password used by Thunderbird when getting new incoming mail and sending emails in the same account/email address.

Maybe the sending smtp server just wants you to login to webmail to confirm it really is you. In which case, the stored password would be useful in trying to get access to webmail.

As you do not seem to have an issue with receiving mail then perhaps that password is already stored in thunderbird. So you can locate that info and use it in the 'Send' password request, then select checkbox for Password Manager to remember password. But are your passwords already in Thunderbird?

'Menu icon' > 'Options' > 'Options' > 'Security' > 'Passwords' tab click on 'Saved Passwords' button click on 'Show Passwords' button This should show you the imap or pop mailbox and also the smtp for that mail account. If you have updated passwords in webmail, you need to update stored passwords in Thunderbird. Right click on appropriate line to see options to edit the password.

Remember, the only place you can modify a password is via webmail account, then update in Thunderbird.

OK, I changed my password via my webmail. Now, how do I get to enter that password in my Thunderbird email settings?

Options-Security-Passwords-Saved Passwords Click Show Passwords Right click and select Edit

I have changed my password twice to no avail.