Last modified: 2014-08-22 19:44:31 UTC
There are sometimes requests to remove private data from mailing lists (e.g. bug 45202). https://lists.wikimedia.org only has the wording "public mailing lists". From my personal experience in other FOSS projects, this isn't clear enough (unfortunately). https://mail.gnome.org/ has an explicit section "My contact details are in your mailing list archives. Will you remove them?". Might be worth to think about something similar, even if it's just one additional sentence.
These are one of the 'annoying hard coded messages' into the software unfortunately. While it is possible to change it; it won't really come with ease. I'll take a look later but no promises :)