"Update Rollup 4 for Exchange Server 2007 resolves issues that were found in Exchange Server 2007 since the software was released. This update rollup is highly recommended for all Exchange Server 2007 customers.

For a list of changes included in this update rollup see KB940006.

This is a cumulative update rollup and replaces the following:

KB930809 Update Rollup 1 for Exchange Server 2007 (KB930809)
KB935490 Update Rollup 2 for Exchange Server 2007 (KB935490)
KB935999 Update Rollup 3 for Exchange Server 2007 (KB935999)"