Hi Andrew! As a general precaution, please be sure you can access your site itself from the network you are using to check your mail. If you seem to be blocked, please check your site with a tool like shotsherpa.com and see if the site can still be accessed from other networks. If other networks can reach your site but you cannot, it is likely that your network has been accidentally blocked by some security software.
If the site is otherwise reachable and, according to cPanel, the email address in question is up and active, you can try checking email deliverability in cPanel for a specific error message, or get in touch with our 24/7 Live Technical Support team for help in tracking down the specific error!