In the settings there is a bunch of server URLs for various peer discovery techniques. I haven’t found too much about their contact discovery but there is at least one issue that hints a central service.
From my point of view (as somebody who wants to use DeltaChat as a chat and not alternative mail client) I’d be strongly in favor of giving contacts with a DeltaChat history a different color.
The Jami setup is just an (optional) keyserver. It is sortof decentralized because it gives you a email-like address, and a keyserver can be run on any domain. I think you can register the same keys on several domains. You type in a person’s email-like address to contact them. Scanning QRs is also an option but I think rarer. Convenience usually trumps security.
It has recently been pointed out that identifying a Chatmail server as such is usually simple. So if someone is using a non-camoflaged Chatmail server, it is easy to tell.
Each Chatmail server could provide an optional keyserver. But I can see good arguements against it.
