This uses a bug/feature in the Paste/Mail macro. Basically, the feature is that a Paste/Mail macro will prevent documents that do not match the selection criteria from being pasted into the database. When documents are mailed in, the docs are placed in the database and then the macro processes the documents that meet the selection criteria. Thus to prevent everyone from pasting documents into the database, you would create a paste/mail macro with the formula:
This would prevent everyone from pasting. Of course, this uses up your paste/mail macro (one per database).