[exim] ACL Sender Verify Problem

Hello,

i try to make my acls going to work, but i fail with the "sender verify"
option.
to construct a little bit clearness in the acls and to just bring up a
simple test of this acl, i introduce a acl only for the sender verify,
effective directly after the "mail from" command:
--------
acl_smtp_mail = acl_check_mail
acl_smtp_rcpt = acl_check_rcpt
...

acl_check_mail:
deny !verify = sender/callout=random
accept

acl_check_rcpt:
...
--------

this wont work..
sender verifying ist executed and everbody from every host with every
"mail from"-part is allowed to inject mail.
the acl-default configuration on my freebsd system with
"verify = sender" in the "acl_check_rcpt"-part doesnt work too.

does somebody can help me to get this running?
i doesnt have the foggiest idea where the failure could be..

thanks for any hints!

regards,
christian