Ian Eiloart writes:
OK. Where do these two email addresses sit?
Addresses aren't relevant. I proposed using List-Ids, which have to be unique (RFC 2919). If an administrator specifies List-Ids that collide, that's not our problem. (The author of RFC 2919 was aware of similar problems, though not this particular one AFAICS.)
Such an administrator will be able to work around it using whatever aliasing mechanism we develop for lists that are gatewayed to and from Usenet.