[exim] Callout

Hi

How can i modify my callout option to resolve problem with:

2010-09-27 11:19:32 H=domain.com [123.123.123.123]:56505
I=[234.234.234]:25 sender verify fail for <sender@???>: response
to "MAIL FROM:<>" from a.mx.domain.com [217.153.18.125] was: 550 5.5.0
Sender domain is empty.

My callout option in ACL:

       deny
                message = Unable to verify sender address ($sender_address).
                !verify     =       
sender/callout=4m,maxwait=4m,connect=30s,defer_ok

I'm a little bit confused, because in exim log i dont see message
"Unable to verify sender address" but default(?) exim warning: "Sender
verify fail"