Hello Quim
Given that this is currently implemented on WMCS, I would think that their
terms would prevail and certain private mailing lists NOT allowed be copied
at all there (for instance a list where checkusers disccussed about vandal
ranges), since it's on an "untrusted" network/servers that shall not
contain such private data. Other private mailing lists may qualify,
depending on what is actually discussed there (e.g. I would see no issue
with a signpost editorial comments mailing list). And obviously, the
content of public lists is simply... public.
Best regards