This is done with Mailbox Manager. I recommend finding some info on this in
Exchange Server Help, support.microsoft.com, or
Here's the short story: In ESM, in the left pane, expand Recipients and
select Recipient Policies. In the right pane, r-click the Default Policy ->
Properties. See if you have a Mailbox Manager tab. If not, close out,
r-click it again -> Change Property Pages. Check the box to add Mailbox
Manager and open the default policy's properties again. This is where you
make the settings.
After that, expand Servers go into the properties of your SBS. On that
Mailbox Manager tab is where you set it to run management.