iCloud Mail and sign-in are both down
Keeping this short and to the point, Apple services are down at the moment and angered users are not too pleased because they are unable to access iCloud Mail and are also having issues with iCloud sign-in.
Even though Apple has confirmed iCloud Mail is down and all users will be affected, they have also list on its system status page that the iCloud Account and Sign-In is having problems as well.
Looking at the Apple system status page you can also see other services are down as well such as iTunes, iBooks Store and App Store. It has been advised all services will resume soon; in the meantime if you are having issues with any of the above do comment.
If you are having issues with iCloud services please comment here.