Yes, worst case quadratic, but redelivered is not resent. Everything is local to the process. In fact, I think the save queue is just a high water mark index a

Yes, worst case quadratic, but redelivered is not resent. Everything is local to the process. In fact, I think the save queue is just a high water mark index at the head of the mailbox. Processing new messages for an existing receive pattern means matching from the end of the mailbox to the HWM. Redelivering for a new receive pattern means resetting the HWM to 0 and rematching everything. So potentially quadratic in matching, but no overhead of copying.