Microsoft offers the Microsoft Exchange Mailbox Merge Program (ExMerge) that is generally used for restoring mailbox stores from one server to another. However, it can also be used in other ways, including the ability to remove selected e-mail messages from the source mailboxes.
This program can be downloaded from Microsoft.
Additional information is located at:
http://www.microsoft.com/downloads/details.aspx?familyid=429163ec-dcdf-47dc-96da-1c12d67327d5&displaylang=en Another similarly useful tool is Aid4Mail: http://www.aid4mail.com/
DLP Storage is capable of scanning pst files. Please see the Admin Guide for more details.
Related: Can Network Discover scan zipped PST files: please see: KB 55353.