#!/bin/sh
# usage: dupl +folder msg ...
#        dupl +folder msg ... | xargs scan
#        dupl +folder msg ... | xargs rmm

delimiter="$(printf '\37')"
format="$(
  printf "%s${delimiter}%s${delimiter}%s" '%(msg)' \
  '%{message-id}|%(addr{from})' '%<(null{list-id})1%|0%>'
)"
prev_key=
scan -width 0 -format "$format" $(pick -search 'message-id:.*' "$@") |
  sort -t "$delimiter" -k 2,3 |
  while IFS="$delimiter" read msg key has_list_id; do
    if test -n "$key" && test "$key" = "$prev_key"; then
      echo "$msg"
    fi
    prev_key="$key"
  done