[exim] smtp transport interface option for deferred emails

Hi,

I am using exim with different IP address (sort of "virtual MTAs"). I use
the *interface* option of the smtp transport to send the emails using the
same ip where they were received.

remote_smtp:
driver = smtp
interface = $received_ip_address
(...)

This works well. But for delivery attempts of deferred emails this doesn't
seem to work fine.
Can anyone confirm this? Any ideas on how to use the same IP for delivery
retries?

Thanks!
Diego.
Exim 4.71