Saving a copy of all bounce messages with Exim4

exim.conf

# /etc/exim4/conf.d/router/050_traffic_tap
# This should be the first defined router.
traffic_tap:
  unseen
  no_expn
  no_verify
  transport = local_copy_outgoing
  driver = accept
  # "mm_domains" is a list of domain names for mailman, e.g.
  # "lists.example.com"; it's set as part of the usual Mailman install on
  # Debian.
  domains = +mm_domains
  # Only do this for bounce addresses.
  local_part_suffix = -bounces : -bounces+*

# /etc/exim4/conf.d/transport/60_local_copy_outgoing
local_copy_outgoing:
  driver = appendfile
  directory = /var/mail/mailman.bitfolk.com/mailarchive/.outgoing/
  delivery_date_add
  envelope_to_add
  return_path_add
  group = Debian-exim
  user = Debian-exim
  mode = 0660
  maildir_format = true
  create_directory = true