[Twisell]

But with a chat app the "classic" behaviour is as far as i know, to guarantee that each participant got all the message they ought to.

Thus what are those billions of messages they store in the database? Is it only a very detailed cache data for current conversation or is it hardwired to PRISM or a commercial database? Why on earth should they store so much chat log?

Or maybe i'm not just not award of the popularity of discord, but Billions of messages volumes make me wonder because as a comparison it's roughly iMessage worldwide per day payload.

So messages are probably stored longer than needed : how and why?

[b1naryth1ef]

The point of our service is that chat is persistent. You can scroll back through time and read all the messages you sent. Users are free to delete whatever they sent whenever if they wish, but for almost everyone persistent chat history is a huge feature. Also important to note that as of the numbers we released last July we receive around 40 million messages a day. The public stats released about iMessage suggest that 2 billion messages are sent per day.

[Twisell]

Can users at least opt-out of persistent chat history? Or define a timeframe after which message are deleted?

You are basically confirming that your company is storing a lot of personal data without user specific encryption. This is pretty scary and I hope you have some improvement about this situation on your roadmap. If not your are a "leak" away from a big problem.

Cool features are neats, but in 2016 privacy should not be seen as a secondary feature...