One of the things that you can do in Enterprise Vault when migrating PSTs is to send out a couple of different messages, to indicate to your users what is happening. The first message is one which explains to the user that they have been enabled for client driven PST migration. The second message is one which tells the user that a PST was migrated.
This small table explains when each gets sent out:
|Server Import||Server Driven||Client Driven||EVPM|
Image credit: Tim Morgan