iCloud Mail issues appear to have started just before 2:00 p.m. Pacific Time, which is around when we here at MacRumors first noticed problems with our own accounts.
Affected users are seeing pop up alerts when attempting to access their iCloud Mail messages. Some alerts are blank, while others let users know there was a problem loading Mail.
At this time, Apple's System Status page is not reporting any outages. It's not clear how many people are experiencing problems with Mail, but not everyone is affected.