mac.com bounces back
when I send an email to my mac.com email address it bounces back. If I'm logged into icloud, I can email from it, but I can't email TO it from another email account.
Does the bounced message give a reason? I assume your iCloud storage isn't full - that would do it. Can you get a friend to try emailing you so that you chan check whether the problem is with iCloud or with the sending account.
With all that checked you should contact Support: https://getsupport.apple.com