Enabling Filter and Forward Mail in Usermin

What's the recommended way to enable "Filter and Forward Mail" in Usermin?

By default, it was activated, but upon logging into Usermin as an Email user and clicking the "Filter and Forward Mail" link, they see:

"Warning - The system is configured to not process user-defined mail filters. Any filters defined below are unlikely to work."

First, assuming I want users to be able to create their own filters, is there some reason not to enable this?

However, I poked around in the various module options a bit and don't see a way to do so.

Thanks!