Per the MYM Rules page: Entering other people’s property is only allowed when the owner has given you the permission to do so. Negative behaviour (Griefing, Theft...) will not be tolerated Constructions, chests, animals etc. belonging to other players may not be moved or destroyed without the owners permission. Items which obviously belong to another player may not be destroyed or moved without permission. So, how do I report griefing and theft?
