There are two ways to set up journaling on the primary mail platform:
a. By defining a specific list of users, whose mail should be journaled
b. By defining a general rule to archive mail for all users.
Use the general rule with the Auto User Creation on Vaultastic enabled if you want to archive mail for all users on the domain. If you want to archive mail only for a subset, define the subset on the primary server.
Mails sent to aliases will also get archived.