Open Tools/Account Settings, select Outgoing Server (SMTP) at the bottom of the left pane and look at all your smtp servers in the right pane. Do they all have connection security set to None and authentication = password transmitted insecurely? If you have multiple accounts on the same domain, it's best to have one smtp server for each account, with a shared user name and password.

This worked and solved the problem. Here's the question I hope you know the answer. Everything was working great for the last two years until this morning. I made no changes, nothing and all of a sudden, this happens and the setting are all screwed up.

Hard to say what happened, as each computer has software working behind the scenes in uncertain ways. Plus, your webhost may have had some hiccups.

Thanks so very much for the help....really didn't want to go back to Outlook

Sorry but it's failing again. It was working fine and now I get...

The message could not be sent because the connection to Outgoing server (SMTP) was lost in the middle of the transaction,.

It appears that something is wrong with the mail server, which you might learn about by contacting your webhost. But some users have had success by deleting the passwords in Tools/Options/Security/Passwords/Saved passwords, Show passwords, Remove, OK to close Options, restarting TB, and entering the passwords when prompted.