Win 8.1 and Win Live Mail Version 2012 (Build 16.4.3522.0110) SMTP Port 587 stopped sending Comcast mail

My email client stopped working today.  

My client has been properly configured as far as port numbers and authentication and has been working properly up until today.  I sent one mail this morning, but subsequent emails failed.  The first failure message said that the Comcast person I was sending mail to was not a Comcast customer.  So I tried a non Comcast email at this point but now it is stuck in the outbox.

I went to my old XP system with Outlook express and sent an email form there to the same Comcast customer - no problem.  I have rechecked that the client accounts on both systems are the same.   

I closed Live Mail and tried to go back in, but it was still trying to send mail.  I ended the process with the Task Manager and then the yahoo client mail was sent.

So feeling more confident, I then tried to resend the email with the Comcast  address.  Keep in mind this address works with the config—Win XP, Outlook Express and the exact same client setup— and I am able to send to the email address, but with Win 8.1 and LiveMail, the response I now get is "Not our Customer".    See full error message below with the person's email x'ed out for their privacy.

The message could not be sent. The setting for your outgoing email [SMTP] server might need to be configured. To find the server settings for '*** Email address is removed for privacy ***', please contact your email service provider.

Subject 'Fw: Humarock'
Server Error: 550
Server Response: 550 5.1.1 Not our Customer
Server: 'smtp.comcast.net'
Windows Live Mail Error ID: 0x800CCC79
Protocol: SMTP
Port: 587
Secure(SSL): Yes

Now this message does not seem to make any sense because I should not need the email settings for the person I am sending mail to.  I searched on  "Windows Live Mail Error ID: 0x800CCC79" which told me to check my email client config settings.  That's it, I've run out of ideas expect maybe a full shut down and restart.

Any assistance appreciated.