delta chat is software for sending chat messages, just like SMS or whatsapp or any of the others. this server, bcc.chat, runs chatmail, which is delta chat server software that facilitates using encryption for all your delta chat messages.
when used with care, delta chat is end-to-end encrypted. so it's much more secure than regular email or SMS, but it's not as secure as signal. however the benefit is that we (regular people who are not large, professionalized organizations) can run it ourselves. this is not the only chatmail server, and with an account on this server you can chat with anyone with an account on any other chatmail server.
to have the best chance of establishing an encrypted chat connection, always scan QR codes rather than typing in someone's username to chat with them. if you've followed all the right steps, delta chat will loudly tell you that you've established a "guaranteed end-to-end encrypted" chat with that person. You can read more about delta chat's encryption model and guaranteed end-to-end encryption.
you should use this if:
to facilitate accessing your account from multiple devices, all messages are kept on the server for seven days. after that they are deleted. however, all the messages will still be on your phone/computer/tablet after they're deleted from the server (unless you don't open delta chat for seven days, then you'll start missing messages).
accounts on this server are not appropriate for sending encrypted messages to regular email accounts, because we do not do IP reputation management for this server because it's too much work.
this server is not backed by a large organization (or any organization) with legal expertise. if your threat model is intense, use signal. if you want to use a reasonably-secure, decentralized chat platform run by regular people, then you're welcome to make an account here or on any other public chatmail instance :)
you can contact us by regular email if you'd like, and we'll make a best effort to respond