Reading Sunbird's site makes it all feel like a scam. Their FAQs and Privacy and Security page are just chock full of what appear to be egregious lies. Both repeatedly state that messages are never stored, and end-to-end encrypted. It is not possible they didn't know this was a lie, because it is fundamentally built in a way that can't have E2E encryption (leaving aside the other horrendous security aspects).
https://www.sunbirdapp.com/sunbird-stance-on-privacy-and-sec...
This quote is nice:
> Some of the messaging community believes that software that is open source is more secure. It is our view that it is not. The more visibility there is into the infrastructure and code, the easier it is to penetrate it.
In my opinion, Sunbird Messaging are fraudsters, and Nothing was their mark.