[exim] interfaces/routing question

Hello!

I haven't been able to find or figure out how to do the following:

We need to have our exim instance _listen_ on multiple interfaces/ip's but we
need to configure it so that it always _sends_ mail through one specific
interface at all times, rather than via whichever interface from where the
smtp request was transacted from.

i.e.

listen on ip's A, B and C
deliver via ip B

Is this possible? How do I do so?

Many thanks!