Most Apple users rely iCloud-related services for most everything. So if you can’t send or receive email, if photos aren’t transferring via iCloud Photo Library, or if some other iCloud-related service isn’t responding, the first thing to do is check Apple’s System Status page. The page reports known service disruptions. If it shows that the associated Apple service is having problems, check the incident details for updates. A newly emerging issue may not appear immediately. If everything is green, it may be a problem with your account or devices, or it just means that Apple is not yet aware of the problem so check back in 10 or 20 minutes.