$ nncp-ack [options] -all
$ nncp-ack [options] -node NODE[,…]
$ nncp-ack [options] -node NODE -pkt PKT

$ nncp-ack […] 4>&1 >&2 | nncp-rm […] -pkt

Send acknowledgement of successful PKT (Base32-encoded hash) packet receipt from NODE node. If no -pkt is specified, then acknowledge all packet in node’s rx outbound spool. If -all is specified, then do that for all nodes.

That commands outputs list of created encrypted ACK packets (NODE/PKT) to 4th file descriptor. That output can be passed for example to nncp-rm to remove them after transmission to not wait for acknowledgement and retransmission.

General workflow with acknowledgement is following, assuming that Alice has some outbound packets for Bob:

Similarly you can use it with nncp-bundle, but do not forget that by default it does not do checksumming of the packets, so you should either use its -check option, or run nncp-check after.