A little pendantic perhaps, but is there any need to support multiple addresses like this? The original thinking for targets was to only define a single 'destination' per target. If you require multiple addresses then you have multiple targets. The only other target that does this sort of thing is 'smtp' and I would argue this should possibly be changed as well. You only need multiple entries for a target if there are multiple parts to that destination address - i.e. mqttpub needs topic, qos and retain details. I don't think this is the correct use of the target addrs map.