A long time ago, a bug existed where a certain combination of policy settings lead to Enterprise Vault's Vault Cache being silently enabled for users when they started Outlook. This wasn't the intention. The real intention was to allows users to manually enable it, when they chose to, or when they were instructed to (via email, help desk, etc).
The issue was fixed in Enterprise Vault 8 SP 3 ... but then became broken again
1) In VAC set the Desktop policies
a) Vault Cache -> "Make Vault Cache available for users" to
"Allow users to decide".
Desktop settings will show OVENABLED = 1
b) Advanced -> "Vault Cache" (Show Setup Wizard) to Off.
Desktop settings will show OVSETUPWIZARD = 0
Make sure that the mailbox is synchronised to contain these values.
2) Start Outlook for the appropriate mailbox.
3) Vault Cache will be enabled silently without any wizard or user interaction.
It has taken quite some time to get the issue re-resolved, but, pending any issues it will be fixed again in the Enterprise Vault 10.0.2 release (never say never, and of course if this is something that impacts you, you'll need to verify the release notes when they become available ... at this time it hasn't been QA'ed, and, this post isn't a committment that it WILL be in the 10.0.2 release << all the usual legal stuff!)
I really just wanted to make everyone aware, that these sort of broken, fixed, broken again type of issues really drive me almost insane, and it makes me really happy when we do get around to sorting them out again.