Anyone could check, "are there any messages for my address?" and you get a whole list of timestamps and encrypted stuff.
Inside the encrypted message is a signature from the sender. That way you 'could' block spam.
Only the owner of the private key could see who sent what, and so...
And even with that my concussion was that users expectations for a private IM might be far away from my experiment.
Bush fire sunsets are the nicest
Some people send "get better" messages, but someone sent me some flowers, so I have something to look at during recovery. This picture shows a white and a pink flower from that bunch.