Due to a persistent error in their mail system, Comcast.net arbitrarily rejects emails for no good reason and doesn't react to emails to postmaster@comcast.net either. It doesn't accept mail from us, for example.

This means, among other problems, that you cannot register on this web site if your email account is at comcast.net.

My recommendation would be to look for a serious, reliable email provider, not for low-quality mass-mailers like Comcast. If you have no other idea, you can resort to Google Mail, for example.