why I can't receive message on my iCloud email

Device or computer?

IOS

Have you tried deleting the account, restarting the device, and then adding the account back?

Mail – Setup on a device    

Mail - If you can’t send email on your iPhone, iPad, or iPod touch

Mail - If you can't receive email on your iPhone, iPad, or iPod touch     

OS

Troubleshooting Apple Mail

What does Mail/Window/Connection Doctor Show? If the server is red, select it and look at the Show Details box.

Mail: Mail troubleshooting 

Mail: If you can’t receive messages.    

Mail: If you can’t send messages.   

Troubleshooting sending email messages    

Mail not sending or receiving messages after updating OS X.