Linux Mail Server Setup and Howto Guide

I'm running a Postfix Amavisd Dovecot SpamAssissin mailserver with hosted email accounts.

Here's what I want to do:

Use SpamAssassin headers with spam scoring and such, to deliver to a user's Spam folder.

At the moment, I have Procmail running, to filter base on those headers into a user's Spam folder and that works fine.

Here's where I'm stuck.

What if the Spam folder does not exist?

I could create the folder during account creation, but a user can delete it from their email client, or rename it.

So, what is the best method to check to see that the folder exists and if not, create a folder owner by that user, so that spam can go into it?