I've seen an error like this when someone had selected the wrong 'Authentication Method' - they had incorrectly selected 'Encrypted Password' Check your Server Settings. Account Setting > Server Settings: Authentication Method: Normal Password

Also make sure the Outgoing Server SMTP also has same Authentication Method.

After making any changes - please restart Thunderbird. Report back telling us what you found - was the wrong Authentication selected ?

re :despite my changing it which when I try to log-in

There is only one place you can change/modify a password and that is via the webmail account. The normal password you use to logon to webmail account is the same password you use in Thunderbird. If you did update the password in webmail account then update the stored password in Thunderbird It's likely that pasword is stored here:

• Setting > Privacy & Security
• Scroll to Passwords section
• Click on 'Saved PAsswords'
• Clickon 'Show PAsswords'

If you get a prompt small window - Windows Security' asking for password then it wants this password - when you start up computer and you enter password to access user account to see desktop - it wants that password.

Then locate the relevant lines for the account. One will be incoming either starting with 'mailbox://account...' or 'imap://account....' and there will also be an outgoing line 'smtp://account...'

• Right click on each line and select 'Edit Password'
• completely clear contents and then carefully type correct password.
• click on 'Close' when done

If still stuck post this info: In Thunderbird

• Help > Troubleshooting Information
• Scroll down to 'Mail and News Accounts' section
• Copy all the data and paste it into this forum question.

Server settings, Password, transmitted insecurely SMTP, Password,transmitted insecurely

These are the setting you should use:

POP Incoming:

• Server name: mail.plus.net
• Port: 995
• Incoming port 993
• Connection Security: SSL/TLS
• Authentication Method: Normal Password
• User name = full email address

IMAP:

• Incoming server name: imap.plus.net
• Port: 993
• Connection Security: SSL/TLS
• Authentication Method: Normal Password
• User name = full email address

SMTP

• Outgoing server relay.plus.net
• Outgoing port 587
• Connection SEcurity: STARTTLS
• Authentication Method: Normal Password
• User name = full email address

Password in all cases is your normal password - same one you use to logon to webmail account.