We're seeing a couple of very large attacks that are targeting a couple of our servers - S0 and S1. While all client sites are online and operational the IPs used for cPanel, Webmail, and most email access are currently un-routed. Due to a misconfiguration in our Anti-DDoS protection that we're working to fix we're not presently able to route those IPs through our Anti-DDoS services. We expect this to be corrected within a couple of hours.
In the meantime you can make the following changes to access cPanel and Webmail.
To access cPanel you would want to access the "cpanel" subdomain on your primary domain. So if, for example, your cPanel's primary domain is "test.com" you would go to "cpanel.test.com" in your browser. You may get an SSL warning but you can safely accept it/pass it.
To access webmail would be similar to cPanel in that you would connect to the "webmail" subdomain of your primary domain. For example if your cPanel's primary domain is "test.com" you would go to "webmail.test.com" in your browser. You may get an SSL warning but you can safely accept it/pass it.
Email Clients [Mac Mail, Outlook, Thunderbird, etc] - if you have them configured to connect to "s0.supportedns.com" or "s1.supportedns.com" you can change this to point to the mail subdomain of your cPanel's primary domain. If, for example, your primary cPanel domain is "test.com" you would connect your mail client to "mail.test.com". You may get an SSL warning from your mail client which you can permanently accept.
FTP - in most cases you can simply connect to your domain name. There are some situations where this wouldn't work such as if you're using CloudFlare or Sucuri CloudProxy in which case you can connect directly to your account IP address. You can find the IP address in your cPanel under 'Server Information' or at CloudFlare or Sucuri.
We do expect this to be resolved within an hour or two so if you just want to wait it out you can. If you do make any changes to your mail or FTP clients - you do not have to revert them.