I have 4 OC810 that are setup to send me an email when motion is detected. It was working very well until few weeks ago. Now the log says 'SMTP: Failed to send E-mail' and when I use the 'Test the Server' button on the E-Mail settings page, I get the following error message: 'Mail server(smtp.comcast.net) is unavailable:sender address is invalid'. I have tried multiple email accounts (Comcast, Google ...) nothing works. Anybody has any idea why it suddenly stopped working? I suspect a change in the Comcast-Xfinity Router-Modem but I can't find what caused it to stop working.