Cannot use smtp.comcast.net as an outgoing mailserver for my private domain

I'm trying to use Comcast's SMTP server to send out my private domain email. I am assuming that if I can log into the Xfinity website and view my Comcast Webmail I should be able to use my Outlook Client to send email authenticated by that same username/password. Email configuration setup is correct per their configuration info. Is there something I need to do to allow the ability to send email? Something I need to activate?