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One of the complaints about the notification overhaul is that many members are email-only, and have no way to mute undesired notifications. The links in message footers are not a solution because they are web links, and one must log in to complete the action.
Granted that logging in is very easy with Groups.io, many members refuse or are extremely reluctant to do so, seeing it as an unnecessary imposition on their enjoyment of group messages.
Converting the message footer links to mailto: links, using new group addresses +mute, +follow, and +unfollow seems like a workable solution to these concerns. The topic number or hashtag in question can be put in the Subject text of the created message.