Microsoft exchange?

Exchange 2003 is available in two versions, Standard Edition and Enterprise Edition. Standard Edition supports one message database per server, and supports databases up to 16 GB in size. Beginning with the release of Service Pack 2, Standard Edition allows a maximum database size of 75 GB, but only supports 18 GB by default; a registry change is necessary to make the database size either larger or smaller than the new default 18GB size. Enterprise Edition allows a 16 TB maximum database size, and supports up to 4 storage groups with 5 databases per storage group for a total of 20 databases per server..