iCloud storage is almost full
Go to Settings > iCloud > Storage &amp; Backup > Manage Storage > under "Backups" select the device you want to free up space on (i.e. "Jim's iPhone"). Go through and turn off different apps that you would like to not backup to iCloud. You can also see the applications that store data in the cloud (i.e. Camera Roll) and how much space each application has in cloud. This should show you where you can go to delete things and free up space. Or you could just turn off that apps backup. 

The iCloud backup list sorts applications with the greatest users of backup space are sorted to the top of the list, so you can quickly assess whether you can thin out the content or need to either purchase more backup space or perhaps disable iCloud backups and instead back up to iTunes and then delete your iCloud backups to allow the space there to serve document sync and email storage.