[Exim] BSMTP and router

hi,

i store some mail for the domain massot.ath.cx in a BSMTP file.
when i actualy want to transfer them, i lauch :

exim -bS -oMr etrn_requeue -oMs massot.ath.cx

which use the following router :
relay_from_file:
    driver = manualroute
    condition = ${if eq {$received_protocol}{etrn_requeue} {yes}{no}}
    route_data = $sender_host_name
    transport = int_smtp
    no_more

I get "unroutable address" bounce message.
If i change "route_data = $sender_host_name"
in "route_data = massot.ath.cx"
it will work perfectly.
why that ? and how can i make it work with a variable expension (because in fact i store mail in BSMTP not only for one domain)

thanks for your help

Edouard

ps : about the ML : why the reply-to is not set to the ML ?
it would be more convegnient dans adding a cc all the time.