Why did you use an inbox for the user's data? I reason it is not the right definition. People hate the inbox. It actually turns them off from using products/services. I've tested it and mentioning the word inbox makes conversions plummet.

I would call it collections, queue, stack, or something else. Even panel.

I do like the process to join in, but I would test the flow through which people create accounts. I'd have them start saving stuff first, then requiring a password to save the data.

Anyhow, good luck