If your OS X Mail mailbox gets full

If you use the Mail app on your Mac to receive iCloud Mail and your iCloud storage fills up, you won’t be able to receive new mail until you make more iCloud storage space available. For more information see:

• Reduce email storage space

• Select which iOS apps to back up

• Upgrade your iCloud storage

Mail on your Mac stores email in iCloud because by default Mail uses IMAP for your iCloud email account.

For more information about using Mail in OS X, in Mail choose Help > Mail Help.