How can I fetch all undelivered messages if reconnect to emitter?

[Dmdv]

Case 1:
A client reconnected and during it's down time, the publisher sends N amount of messages.

How can I provably fetch all unprocessed messages after the consumer has restarted?

Case 2:
Consumer got a message but failed to process, exited and restarted.
How can I provably fetch the same message where it stopped?

Do you support ACK?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.