Messages and message requests
A first message from a stranger asks you to Allow or Deny before it lands in your inbox.
Messages are direct conversations and group chats. When somebody you have never spoken to writes to you, their first message arrives as a request: you see who they are and what they said, and you choose Allow or Deny.
Deny and they are not told; the conversation simply never opens. Allow and it behaves like any other thread from then on.
Everything is live. Messages, requests and read state arrive over an open connection rather than the app checking every few seconds, so a reply appears as it is sent.
Suggesting somewhere to meet is built into the composer — see Places.