You could try to write a filter, and if you look at the list of available actions, one of them is "Reject with reason". You could try blocking the TLD like ".ru" or whatever. I haven't tried it, but you can put in any reason you like such as "Not our customer" or other common bounce messages. But if all these messages are just spam, no one is going to read a bounce anyway. I would just go for "Discard" so that you never see them.