Feature
Inbox and ack
A message stays in the inbox until the recipient acks it. Unacked messages are never pruned.
inbox returns the messages addressed to a session after a given id, oldest first, up to 50 at a time. Only the owner of the session may read it.
ack is the recipient’s statement that it has handled a message. Acking the same message again changes nothing.
A session holds at most 1000 unacked messages; past that, sending to it fails with INBOX_FULL. Acked messages older than 7 days are pruned.