[exim] Hiding the sender in an exim-run mailing list

Hi, I have a number of mailing lists set up for a number of virtual domains, in the following fashion (from directors config):



lists:

domains = /etc/exim/exim_virtual_domains

driver = forwardfile

# no_more

require_files = /db/virtmail/lists/${local_part}.${domain}_VALID_SENDERS

senders = lsearch;/db/virtmail/lists/${local_part}.${domain}_VALID_SENDERS

file = /db/virtmail/lists/${local_part}.${domain}

no_check_local_user

forbid_pipe

forbid_file

rewrite = true

errors_to = admin@???



So, only people who are in a ${local_part}.${domain}_VALID_SENDERS are allowed to send messages to the list; I would like to change the senders' addresses (say, to admin@domain), so that recipients do not know who sent the message; but i want the addresses rewritten ONLY when a message is sent to a mailing list; in other cases, the original sender's address should remain. How to do that? I'm runing exim 3.35



Thank you, Mik Kocikowski, Adam Mickiewicz University, Poznan, Poland.