When Apple's MobileMe suite of online services got revamped and changed into iCloud, existing members were provided with 20GB of extra storage space compared to the 5GB normally allotted, for a total of 25GB (which includes email storage, iCloud iOS device backups and other services such as Documents in the Cloud). The company has now sent out reminder notices to such customers letting them know that the additional free storage will be withdrawn and reduced to the standard 5GB on September 30.
