Problem started with Thunderbird update installed today. Checked with provider, which recommended changing the port address. This was done. Rebooted computer, modem and router. Tried sending with firewall & virus software disabled. When trying to send, the sending status dialogue box appears normally, and shows the completion bar as 100%, but no send confirmation appears. Closing the box reveals the "message failed to send" notice. Tried to upload a screen shot, but your web site did not complete the upload.