smtp.comcast.net stopped taking outgoing emails late Feb 2021

I use a pop3 client (Windows Live Mail) to communicate to smtp.comcast.net.  I have the settings set per comcast documentation... they have worked for years.

Recently outgoing email transmits (with NO error) but do NOT arrive. I can send from the xfinity email page with no problem. Pop3 clients no 2 different computers are having the same problem.

Has a certificate changed ??  I get no error message.