If iCloud Mail isn't working — perhaps you can't log in, send, or receive email, or doing so is slow and glitchy — check the iCloud system status. Here's how.
Check iCloud's System Status
Open Apple's System Status page.
Locate iCloud Mail in the list.
If the circle next to it is green, then Apple is reporting that iCloud Mail is running normally from their end and should be fully available for you. If the link is blue, select it for more information about a recent problem that caused iCloud email to stop working.
How to Report an iCloud Mail Issue
If your problem is not listed, report it to Apple:
Open the iCloud Feedback form.
Enter your name and email in the first two text boxes.
Entering your email address is optional but gives Apple a way to respond if they need more information or have information to share.
Put a one-line summary of the iCloud email problem in the Subject field.
Choose Feedback Type > Mail.
Include as much detail as possible in the Comments area: why you think iCloud Mail isn't working, what you've already tried, what you were doing when you noticed the issue, and what you expected to happen that didn't.
Fill out the remaining fields in the feedback form and choose Submit Feedback.