Cannot send email SMTP error

I can only send mail using my online Comcast email account. I cannot send with eM Client or with Thunderbird. I have tried turning off my VPN, but that made no difference either. I have tried everything suggested by Comcast, and checked every setting over and over. Very frustrating when you run our of things to try. This only started a few days ago and nothing has really changed that I can think of that would cause this. Unless the SMTP on Comcast is the problem.?

So this is not an eM Client problem? Did you manage to solve it?