BM-2D9tpN1g82FC9hhC8eof5BiH3Dc2NCTzQ6
Just tested it by sending a message to someone from Reddit. They must not be on though, no reply. My understanding is that eventually, if he does not reply the message vanishes?
If he doesn't come ONLINE, the message disappears. They can only be downloaded dependably for two days after they are sent.