Exchange 2007 SP1 has a default transport database cache size of 128MB. This size doesn't allow as much dynamic growth as may be necessary on Hub servers with higher than normal message rates, or when an unexpected load from increased message size comes into a server. To better allow for cache growth, the new guidance is to increase the DatabaseMaxCacheSize value from 128MB to 512MB on Hub servers with 4 GB or more memory installed.
In Exchange 2007, the transport service utilizes the Extensible Storage Engine (ESE) for mail transport functionality. This provides several benefits over previous versions that used the NTFS file system: