Comment by Almondsetat

A protocol can only support, never mandate. If I send you "DELETE MSG #4829" and you do nothing and reply with "200 OK; DELETE MSG #4829", nobody observing the protocol's messages will ever know what happened. Sure, an omniscent being could say "but he internally broke protocol, he didn't delete the message!", but by definition if something cannot be verified inside the protocol, it is outside of protocol.