[Dovecot] Making shared folders "unmovable"

I have set up an area of shared folders with Dovecot 1.2 that is accessed by several people (by way of one account, and everyone who logs in sees these same folders), and the only problem with this setup is that occasionally somebody moves one of the folders underneath another folder or somewhere else in the folder structure, and this sometimes disrupts some automatic procmail filters and the like.

Is there a way to keep folders in a shared setup such as this "static" or "unmovable" so that the users can't disrupt the structure? Like, where the folder structure itself can't be changed, but new messages can still come in to the folders?

David