'approved' rule should not modify the message
Original LP Author: Barry Warsaw , LP Link: https://bugs.launchpad.net/bugs/973790
In Mailman 3, technically rules should not have side effects. The 'approved' rule breaks this because it removes the Approved header (and other supported headers) from the message. There should instead be a handler that does the header cleaning, and the rule should not do this.
From an implementation standpoint, the same code can be used in both the handler and in the rule. You can use a slightly different API wrapper and use a flag to indicate whether the header should be removed or not. OTOH, some clever refactoring might make better sense.