Exchange Server 2003 is available in two editions:
Exchange Server 2003 Standard Edition is designed to meet the messaging and collaboration needs of small and medium-size corporations.
Exchange Server 2003 Enterprise Edition is designed for large enterprise corporations and enables you to create multiple storage groups and multiple databases. Exchange Server 2003 Enterprise Edition provides an 8-terabyte (TB) public folder store that eases the constraints on the amount of data that a single server can manage.