text: create table string (
    id integer not null primary key,
    val string unique
  );
  create table message (
    id integer not null primary key,
    parts integer,
    msgid string
  );
  create table header (
    id   integer not null primary key,
    ord  integer,
    mid  integer references message,
    ksid integer references string,
    vsid integer references string
  );
  create table payload (
    id integer not null primary key,	
    mid integer references message,
    ord integer,
    typ string, -- mime type
    val string
  );
  