In earlier version of exchange where streaming backups were supported, checking the integrity of the database was part of the backup process. Now with the new high availability features in exchange 2007 like CCR, it is possible to take a backup of the passive node thereby reducing the load on the active cluster node.
What this means is that the integrity of the active database is not checked on a regular basis, unless the admin flips the active node frequently or the database is dismounted & eseutil command is run against it. Both the options are not practical. Hence, in exchange 2007 sp1, database checksumming (checking the database integrity) is included in Online Maintenance. But, it is not enabled by default. Anyone who needs to run the integrity checks daily has to add a DWORD name “Online Maintenance Checksum” and set the value to 1. Information Store has to be restarted for this to take effect.
The snapshot below shows the location in the registry where the DWORD has to be added.