Outlook rules with separate PST

Hi

My client had too many emails within his inbox so we reorganized his Outlook in order to store emails in a separate PST file, a simile archive if you will.

Outlook is configured with half a dozen email accounts and previously rules sorted and stored emails into their respective folders, which were present within the inbox

Now that these folders have been moved to a separate PST file the rules aren't working anymore

Any idea why ? Is this by design ? any workaround ?

thanks
yann