Domain Administrator can specify Domain-wide Rules.
When a Message is being delivered to any Account by the Local Delivery module, or when a Signal targets any Server Account, the "effective" set of Account-level Rules is applied. The first Rules in the effective set are Domain-wide Rules with priorities above 5, then it includes all Account-level Rules, and then - all Domain-wide Rules with priorities equal to or less than 5.
This method guarantees that all Domain-Wide Rules with priorities higher than 5 are applied before any Account Rule. If such a Domain-Wide Rule uses the Stop Processing action, no Account Rules are applied.
Note: Domain-Wide Rules are "mixed" with the Account Rules and are applied in the same environment as the Account Rules, "on behalf" of the Account user.