Optional ReadonlyloggerThe logger (default the client's logger).
Optional ReadonlyonCalled with every entry that failed permanently.
Optional ReadonlystoreThe storage (default MemoryOutboxStore).
Optional ReadonlytokenReturns the newest invocation token of a run. With it, an entry of a run goes out bound to
that run (07 SR9) whenever it is sent, also from a later flush, and an entry of a run
without a known token fails instead of going out unbound.
Options of Outbox.