You need an international copyright lawyer. This is a fraught topic.
On list email, I recently set up a big sophisticated mail server to support GNU Mailman 3 mailing lists, and moved an archive from a previous list with 100,000 posts across. Extensive discussion with my colleagues in that project revealed that, surprising to me, it appears to be the legal consensus that the poster of the email owns the post and its material in a strong sense, and posts are not the property of the list or the list owner,. and that duplicating posts for archival purposes can therefore be in violation of various parts of copyright and intellectual property law, and the whole business is a nightmare. Going against this however is the norm that I think most members of mailing lists like my harpsichord list and this lilypond list feel that their posts become 'public domain', meaning not subject to copyright, as the intention generally is to share and discuss.
I am in Australia, and our copyright/IP law is different to the US, and to Europe, so I cant really comment any more. But this appears to be an infinitely deep rabbit burrow to explore.
Looking at the spirit of sharing, I feel pretty sure that people who contribute to openlilylib, and to LSR, and who post code snippets and solutions here on this list intend these works to be shared and used by all, despite what the letter of the (internationally varying) law may be.
Andrew