Metadata is most hideable (but still exists) in a crowd. At scale (i.e. millions of users) an improved version of shared shared mailboxes like alt.anonymous.mes

Metadata is most hideable (but still exists) in a crowd. At scale (i.e. millions of users) an improved version of shared shared mailboxes like alt.anonymous.messages can be effective. I reckon that it can be effective at a lesser scale if initial participants all generate enough random noise to protect anonymity of the first users to adopt the system. Once it has scaled in users, they can scale back the random noise generated.