Mailboxes are a queue of messages with guaranteed ordering. Mailboxes have a set of useful properties that make them really powerful:
- Mailboxes are partitioned. It means that messages are distributed through partitions, and subscribers can read from different partitions.
- Mailboxes are dynamic. You can subscribe and unsubscribe from a mailbox many times.
- They guarantee ordered/only once delivery. Even if an actor can process the same message more than once (depending on the recovery strategy), the message will be only delivered once by the mailbox.