One common reason for Comcast email problems is server outages. If the server is down, you won’t be able to send or receive emails. Another potential issue could be incorrect login credentials. Ensure that your username and password are entered correctly. If you need help resetting your password, call +1-855-200-5156 for guidance.
Source: https://support.us.edu/hc/en-us/community/posts/26990777466903--M-855-200-5156