Hello, my Cox email account was migrated to Yahoo mail. I can receive emails but now I can't send emails from Thunderbird. I've triple checked server settings. Please help. Thanks-Vince This is the message I get and it does this with all email addresses. Sending of the message failed. An error occurred while sending mail. The mail server responded: Request failed; Mailbox unavailable. Please verify that your email address is correct in your account settings and try again.