[Exim] conditionally setting Return-Path

Hi everybody,

a customer of ours (running exim 3.35 on Debian) wants the Return-Path
header to be changed to customer@address for all outgoing mails that
have a header "From: realname <customer@address>".

I tried the following which didn't do the job.

Transports

returnPathSmtp:
driver = smtp
return_path = customer@address

standardSmtp:
driver = smtp


Routers

returnPathSmtp:
  driver = lookuphost
  transport = returnPathSmtp
  condition = \
      {if match{$header_from:}{customer@address}{yes}{no}}

standardStmp:
driver = lookuphost
transport = standardSmtp


Unfortunately, the Return-Path is always set, debugging indicates the
returnPathSmtp router is always used


Any ideas what's going wrong?

Thanks,

Martin