As many people already know Enterprise Vault uses a number of hidden messages in an end-users mailbox to store information about settings and policies in place. The Vault Information dialog shows those hidden messages, for example :
HIDDEN MESSAGES IN FOLDER Inbox
IPM.EnterpriseVault.Filter:
Last modification time 11:00:18, 06/07/2010
Archive ID 1850CAB7BBD94E4498E2A27FCDD5EA95E1110000w28ksrv.EV.Local
ArchiveFolderId 16F8F77E1B1406C43A9B38E7C5EFFFAB81110000w28ksrv.EV.Local
IPM.Note.EnterpriseVault.Settings:
Last modification time 11:00:18, 06/07/2010
;MAILBOX; vctest
;SERVER; EXCH1
ALLOWSCRIPTPUBLICFOLDERS 1
ALLOWSCRIPTSHAREDFOLDERS 1
APPLICATION_PATH c:\program files\enterprise vault\evclient\
ARCHIVEDELITEMSFOLDER 0
ARCHIVEEXPLORERBTNVISIBLE 1
ARCHIVEMANAGEDFOLDERS 0
ARCHIVEONLYWITHATTACH 0
ARCHIVESETTINGSLOCKED 1
...