[exim] callouts and tls

Hi

I need to do callout verification.
My front-end server is an exim 4.63 (debian etch), the back-end is an
exchange 2003 server.
That server is reachable on a no-standard-port with tls only.

I have the following router and transport:

relay_x:
driver = manualroute
domains = domain1 : domain2
route_data = 1.2.3.4::10025
transport = remote_anytls

remote_anytls:
driver = smtp
interface = 80.190.243.78
hosts_require_tls = *

This works well for delivery.
However callout verification fails.

  warn    domains        = +local_domains
          !verify        = recipient/defer_ok/callout=10s,defer_ok
          log_message    = recipient callout failed: $acl_verify_message
$recipient_verify_failure

I get:

2008-02-19 11:33:22 H=mailhub.netex.ro [193.178.141.9] Warning: recipient
callout failed: mail

I assume this happens because the exchange port is configured to require
starttls before mail.

Can I do anything here?

Regards,
Steffen