[Exim] Archiving outgoing e-mail for some user

I have been asked to archive any outgoing message (incoming is
trivial) for an office.
I have to explain: this office is manned by 9 different people during the
week, so a job could be continued by a different person. It is essential
that ANY message sent from them be archived, to avoid an accidental
deleting. any of these message arriva with a from: field as
fl-name@???
where name is the originator name to ease handling or replies.
I wish that any outgoing messages whit a from of the type fl-*
will be forwarded to another (fixed0 address, possibly unless that fixed
address is the rcpt address ...), beside the original recipient (unseen
rule?!)
I could use it either at smtp level or at director level ...
suggestions ?
(i have to process according the from part, not the rcpt !)