iCloud: Check available email storage
Your iCloud account includes 5 GB of free storage for your mail, documents, account information, and the iOS settings and app data that are automatically backed up by iCloud.
If necessary, however, you can purchase additional storage.
See how much space is available in your iCloud mailbox
On your Mac, choose Apple Menu > System Preferences, click iCloud, then click Manage.
On your Windows computer, open the iCloud Control Panel, then click Manage.
To open the iCloud Control Panel in Windows 8, move the pointer to the upper-right corner of the screen to show the Charms bar, click the Search charm, then click iCloud Control Panel on the left.
To open the iCloud Control Panel in Windows 7 or Windows Vista, choose Start menu > All Programs > iCloud > iCloud.
For help managing your storage, go to Troubleshooting Storage on the iCloud Support website.