As taken from here..

We have released Update Rollup 9 for Exchange Server 2007 Service
Pack 1 (KB 970162) to the download center. The release of the rollup
via Microsoft Update will happen on July 28.

The majority of changes in this rollup are bug fixes. Here are a few that I would like to call out:

  1. KB 969911 – This is bug likely to affect customers who have deployed the Messaging Records Management
    feature and have specified a storage limit for a managed folder. After
    a move mailbox, the property which marks the folders as managed is not
  2. KB 968621 – Store stops responding under certain conditions when scheduled backup is canceled and online maintenance is in progress.
  3. KB 945877 – Performance improvements to eseutil when it verifies the checksum of transaction logs.
  4. Support for Windows Server 2008 R2 Domain Controllers in the
    environment (Note: Exchange Server 2007 itself is not supported to be
    installed on a Windows Server 2008 R2 system.
  5. KB 968715 – This bug is likely to affect customers who have deployed CAS-CAS proxying. When a user selects This is a public or shared computer or This is a private computer
    on the Outlook Web Access logon page, this value is not maintained 
    between the CAS servers when the request is proxied. This bug will most
    likely affect customers with Internet facing CAS sites which proxy the
    requests to internal sites. Now the bug was that we defaulted to
    private access irrespective of the option selected by the user. Outlook
    Web Access has the following features which allow the administrator to
    control access of users depending on the logon type.:
    Public and Private Computer File Access
    WebReady Document Viewing