Using Thunderbird with Xfinity email, sending an email gets the below error message. I contacted Comcast and we went through troubleshooting and could not find any problems on their end. They suggested I contact Thunderbird support. Here is the error message: "Sending of the message failed. An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: resomta-po-11v.sys.comcast.net resomta-po-11v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available." This problem does not happen all the time but frequently.