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

match='%<(null{list-id})1%|0%> %{message-id}|%(addr{from})'
prev_key=
scan -width 0 -format "%(msg) $match" "$@" | sort -k 3 | sort -k 2 |
  while read msg has_list_id key; do
    if test "$key" = "$prev_key"; then
      echo "$msg"
    fi
    prev_key="$key"
  done