locked preventing add -abuse
People, I don't think proving you have a an existing groups is enough. We need to have some way of "punishing" people who abuse the "add members" feature.
The easiest one I can think of right away is to have something in the "you've been added" message like:
groups.io does not want to spam. If you have been added against your will, please notify [email adress] instead of flagging the messages, so we can take the proper action against the abuse
Obviously, the person at that e-mail-adress should give the abusive listowner/moderator one or two warnings, and if they persist.. close the group