Naven
Glossary
Direct message
A private conversation between two people.
The default unit of most messengers, and the one with the fewest design questions. The interesting parts are at the edges: whether a stranger can start one, whether the recipient is told who is asking, and what happens to the conversation when one side blocks the other.
Allowing anybody to DM anybody is the single largest source of harassment on platforms that do it.
Where Naven stands
On Naven a conversation is started by an email address or username somebody already has. There is no directory to browse, so a stranger cannot find their way to you by name.