[exim] Recipient verification callout

Hi,

    I'm setting up recipient verification for some external address to 
servers for which I'm doing antivirus filtering. Since I don't have the 
list of valid address I would like to perform a recipient callout, so I 
can reject mail for invalid users at SMTP time.

In acl I set recipient verification:

accept  domains = +local_domains : +relay_domains
        endpass
        message = Unrouteable address
        verify = recipient/callout=2m,defer_ok,use_sender

Then I set up a router with manualroute driver:

av_gateway:
driver = manualroute
retry_use_local_part
transport = route_to_external_host
route_data = ${lookup{$domain}lsearch{/path/av_gateway.txt}}


Now, when I test this configuration with exim4 -d -bhc I receive this
answer:
...
routed by av_gateway router
envelope to: test@???
transport: route_to_external_host
host xxx.xxx.com [xx.xx.xx.61]
host xxx.xxx.com [xx.xx.xx.162]
Cannot do callout: neither router nor transport provided a host list

What am I missing? As suggested in docs (38.21 Callout verification) I
set up a manualroute so I have hosts specified, but it seems that (at
least in testing mode) this doesn't work.

Regards
---
Igor D'Astolfo