If I remember correctly, Findmail does not go out and actively or automatically
look for external mailing lists to archive, but they do provide a Web interface
where individual USERS can enter the name of a mailing list and ask that it be
archived. If one of your mailing lists appears on Findmail, it's probably
because some interested subscriber put it there.
I agree that it would be much nicer if the result of a user request for an
external archive was an email sent to the owner of the list in question saying,
"User <address here> has requested that we archive your list <so and so>. If
this is OK, please reply to this email with the word "yes" in the message body;
any other response, or no response, will result in no archiving."
Carl Page's suggestion, that concerned listowners start using X-No-Archive all
over the place, has one enormous problem, which is that LEGITIMATE archives for
your list may exist, with access rights and format of your choosing; this
"industry standard" cuts both ways.
Personally, I would watch (using Procmail) for subscribes from findmail.com, and
kick them off immediately, and then send that "listsaver-of-" address just ONE
message for its "archive" saying: THIS IS NOT THE REAL ARCHIVE. This was created
without permission. Tell Findmail to stop operating this way." A wave of those
ought to generate enough user feedback to get them to think about the issue. :)