thunderbird client failure

Without any warning or indication my thunderbird email client stopped receiving emails. Only after checking the web based email did I notice new emails were in the Inbox. No settings were changed on the client, it has been working for years. Attempts at sending a message now return this message. Sending of the message failed. Peer reports incompatible or unsupported protocol version. The configuration related to smtp.hughes.net must be corrected. credentials were verified, using smtp.hughes.net Port 587 Auth normal password conn security STARTTLS thanks in advance