Date: Wed, 18 Sep 2002 15:22:44 +0100 (BST)
From: Tony Finch <fanf2@cam.ac.uk>

I wanted to be able to preserve the envelope contents (except for the return
path when I'm feeling paranoid about error handling).

Feel free to add this to the examples -- someone else might find it useful. I
also have a complete configuration which I have been recommending to other
people in Cambridge (although it could work elsewhere with tweaks) at
http://www-uxsup.csx.cam.ac.uk/~fanf2/conf4.satellite.

# Deliver a duplicate of some proportion of all messages to a special
# machine specified in the file /MAIL_TAP_HOST, if it exists. The
# probability of sending a message is the reciprocal of the second
# number in the hash part of the condition. The address data is used
# to prevent redirected addresses from being tapped twice. The
# originating host and sender are recorded in extra headers. If the
# delivery fails the bounce goes to a rubbish bin (although this means
# that the traffic seen by the tap is not quite the same as the
# traffic seen here).

traffic_tap:
  unseen
  no_expn
  no_verify
  transport = smtp
  driver = manualroute
  require_files = /MAIL_TAP_HOST
  route_data = ${readfile{/MAIL_TAP_HOST}{:}}
  address_data = ${if!def:address_data{tapped}fail}
  condition = ${if!eq{a}{${hash_1_1:$message_headers$message_body}}{no}{yes}}
  headers_add = ${if!def:sender_host_address{}{X-Orig-Remote-Host: $sender_host_address}}\n\
                X-Orig-Return-Path: $return_path
  errors_to = YOUR_RUBBISH_BIN_ADDRESS_HERE