[exim] Whitelisting some senders not working

Debian Sarge box, exim 4.50

/etc/exim4/exim4.conf
---------------------
acl_check_rcpt:
[...]
deny   message     = Access denied
       log_message = Blacklisted sender
       senders     = ! CONFDIR/whitelisted-senders : \
                     CONFDIR/blacklisted-senders

CONFDIR/whitelisted-senders
---------------------------
[...]
sentto-123456-*@???

CONFDIR/blacklisted-senders
---------------------------
[...]
*@somedomai.com


If I send a message (exim4 -bh) from
sentto-123456-whateverstring@??? I always get
access denied. The sender never match the whitelisted-senders rule.

Any hint will be welcomed.

Is it a better way to achieve whitelisting some specific addresses
in a domain and blacklisting everything else in that domain?

Regards,
maykel