Looks quite interesting. What did you create this with? I think you should have a better intro and maybe some video or something to outline what it is without people needing to log in
Encryption wise, I'm using CryptoJS for AES256 and OpenPGP.js for PGP.
All messages get encrypted in AES256 with a randomly created passphrase. The passphrase is then distributed to the recipients using PGP.
Keep MongoDB on it's own server.
Other than that, nice idea.