When an outgoing ack has a ratchet mismatch then it will fail to send but remain in the outbox thus blocking the entire outbox queue... preventing any other messages from being sent to any other contact.

Shouldn't we provide a way to delete outgoing ACKs (unmerged acks)?

(I had to write code to remove messages from my outbox in order to get my pond client to send messages again... but normal people would just give up I think.)

Or if an ack fails to send it should be removed from the queue if it results is a key mismatch error... so that it doesn't prevent other outgoing messages from being sent.