I have been using Thunderbird for decades, without a problem. All of a sudden, two days ago, I am not able to send emails. I receive a pop-up alert which says, "An error occurred while sending mail. The mail server responded: 5.7.1 <my email address is entered in brackets>...Local senders are prohibited to send to local recipients without authentication. Please ensure that you are using the correct identity to send and that the used authentication method is correct. Verify that you are allowed to send via this SMTP server with your current credentials from your current network." It appears that my settings are all correct, but for three days I have been unable to send emails. I have restarted and performed hard restarts without success. Can anyone help me.