I would feel a bit misled if most of the internal mailing lists I've been on were ever made public. I suppose it depends on the size, though. I've been on research-group mailing lists of ~10 people, and that would really feel like a breach of confidence, to release to the world at large emails that were intended for a relatively small circle of colleagues. On the other hand, if someone made a 200-person mailing list's archives public, then I would probably not be as annoyed.