IMPORTANT: This post contains ideas intended to spark discussion and gather feedback. These are not final concepts and must not be interpreted as implementation details. For official information about how XMTP works, see the XMTP technical documentation. Have questions about this post? We’d love to hear from you—post a reply.
I’m a developer looking to build on XMTP. I just checked out the xmtp.chat and I want to confirm something. So I can’t message an address not registered on XMTP ?
Hey there! Welcome to the XMTP community! 
You’re absolutely right - you can only message a wallet address that has already registered with XMTP.
When someone first wants to use XMTP messaging, they connect their wallet to an app built with XMTP (like xmtp.chat) and sign a message to create their XMTP inbox and identity. Once they do that, their address becomes “XMTP-enabled” and can receive and send messages.
If you try to message an address that hasn’t done this setup yet, the message isn’t deliverable because there’s no inbox and identity to deliver it to.
I hope this helps! Please feel free to ask if you have more questions… 