A script to manage incoming mail

So since at http://wiki.dreamhost.com/Procmail it is written that

“This no longer works due to a system change as of April, 2008. New and existing email address may no longer be tied to a shell user if they are not already”

how do I setup a script to manage incoming mail?

Is there any way to do this?

Scroll down a bit in this blog entry for instructions: