When I send a message in Thunderbird using a Yahoo.com server, I get the error message attached and the message I just sent disappears. I can't find it in Sent or in the Inbox if I reply to an incoming message or in the Drafts folder. When this first happened, I repeated the send three times before checking the Yahoo email window. All three of my Sends were recorded there, but none in my TB Send folder. How can I fix this?