To find your Comcast (Xfinity) email address go to Xfinity.com and Sign In.
Click on the Mail (envelop) icon in order to open the Email Web app. You can receive and send emails right here without Mail client on PC or phone.
Now click on the Tool icon and then Settings.
Then click on Accounts on the left and click on Edit next to Email.
In a pop-up window, you will find your Comcast email address.