Okey, so relays can pass message to other relay? Didn’t know that, so thanks.
Relays currently don’t talk to each other. But users are typically connected to multiple relays and publish simultaneously to multiple relays. Likewise, a user pulls in data (tweets etc) from multiple relays. My client is connected to ten. So to give you a more accurate answer to your question, to DM another user, you and that other user need to share a relay. If you are crossing networks (such as clearnet->tor), this means one of those relays needs to talk to both networks. If you want to follow a particular person but aren’t normally connected to a relay they are on, your client can connect to a relay just to get content from that particular person. All of this is handled automatically, of course.
But then, why not use network like Yggdrasil? Which would be basically like Nostr, but can relay any TCP/IP packet for any app, instead of just Nostr notes.
Taking a cursory look at this, it sounds more like a general routing protocol not something that is specifically designed to relay message content or other formatted data (ie you build your apps on top of it, it’s just a protocol for packet delivery). Nostr could conceivably run on any base routing protocol like Tor, I2P, or Yggdrasil though I don’t know of any specific implementations either way. As long as the relay has a way to resolve addresses and send data to them over TCP it should be fine. Hadn’t heard of Yggdrasil yet thanks for letting me know about that I’ll do some more reading later.