Quite often end-users make use of Virtual Vault to archive things that they no longer need in their mailbox. How do they do this? What happens to the Virtual Vault files? Let's see...
First of all, as we all know, Virtual Vault and Vault Cache work in tandem. Virtual Vault itself really consists of just a metadata cache (the MDC file). If you have that, then you have Virtual Vault in your Outlook mailbox profile. Here is one for my test user:
When I drag and drop some items from my mailbox into Virtual Vault, what happens to them?
First of all, they are added by the Enterprise Vault Outlook Add-in to the MDC file. Here you can see the size difference from the previous screenshot, after I dragged and dropped a folder from Outlook into Virtual Vault:
At this point that might be all that happens. You can see the items which are waiting by looking at the synchronisation window:
In the background though the next time the Vault Cache synch operation runs the items will be sent to the Enterprise Vault server for actual archiving. And on the synch after that, the items will become 'just' stubs again in the MDC file.
The MDC file though won't shrink in size. It's one of the things with 'all' PST files; they don't automatically shrink when data is removed from them.