There needs to be a user forum message at least as soon as you reach your inbox limit, maybe on your wall or something from a bot admin or something. Right now it looks like you don't get any message until you've already missed out on at least one private message and it's through e-mail and it can be sort of inconvenient.
Is there some kind of premium membership available where we can have a larger inbox capacity? I think that would be really great and I would happily pay some kind of premium for unlimited inbox storage. I don't like deleting messages because it helps me keep track of where all my traded pokemon came from. The inbox capacity is really small and I think an option to upgrade it (and maybe some other fun features as well) would be great.