Message bug, please fix

Fix this please. I often get notifications saying I have a message, yet when I open it the message is gone. I assume the app just deletes it because I never receive a message from that person again. It would be nice to add people to a friends list or something instead of relying completely on the app for whether you can ever talk to them again. Thats kind of crappy.

Kawaii-desu about DokiDokiPostbox