It uses SMTP/IMAP to propagate and store individual messages. This means that DeltaChat it will work with your usual email account (it will create an IMAP folder named DeltaChat), but if you install the app and say “Yeah, just let me in!”, it will create a random username for you on one of its own chatmail servers.
It may sound like a bad thing to use email, but it works very, very well. Most people won't even notice.
See e.g.:
Kinda surprised to find this on privacy policy of the default chatmail instance:
> unconditionally removes messages after 20 days
Didn't see any warning about this in the GUI or the chatmail page.
Does this mean after 20 days the messages on my app will disappear? or just they'll only be available on my local app after that point?
In any case, that's a pretty big red flag that it's not clear.
https://delta.chat/en/help#what-happens-if-i-turn-on-delete-...
https://github.com/chatmail/relay/blob/96a1dbac08441034c5990...
https://github.com/chatmail/relay/blob/96a1dbac08441034c5990...
You obviously must trust that the server runs this configuration, but you can always run your own chatmail, or regular postfix. (If you don't need "federation" with other mail servers, you don't even need port 25 open).
However, you can also configure your app to delete messages from the server sooner.
»By default, Delta Chat stores all messages locally on your device. If you e.g. want to save storage space at your mail provider, you can configure Delta Chat to delete old already-received messages on the server automatically. They still remain on your device until you delete them there, too.«
https://delta.chat/en/help#what-happens-if-i-turn-on-delete-...