I have had this problem contiually - to the point, I have PAID for another email address to get around this issue (which I should not have had to do, being as I am paying already for the comcast.net address). This is VERY frustrating!
The ISSUE IS:
Whenever I go to website, to create an account, sign up for an event, etc. where one is required to enter their email address, when I enter my comcast.net address, I get the RED exclamation point next to the email address box and an error stating: "enter a valid email address". And YES - I have entered my email address CORRECTLY (multiple times). I have had other friends with comcast.net addresses complain of the same problem. What is the ANSWER to this??
Solved! Go to Solution.
If your Comcast email account functions OK otherwise, there is nothing wrong with the account. That means the issue is at the other website. I have used my Comcast address to sign up for quite a few things and have never encountered the problem you describe. That being said, just use some other address from a free email provider like Gmail, Mail.com, Outlook.com or others.