[exim] sender verify callout

Hello,

I have a question about how exim does sender verify callouts.

Based on my testing, it appears that exim always uses the incoming host
(or incoming IP address) for doing callouts. That is, it appears that
exim always connects directly to the host that initiated the smtp
session for doing the callout. Could someone either confirm or refute this?

If that is the case then I have a second question: Is their a way to
force exim to use the domain MX record for callouts instead of going
directly to the incoming host for the callout?

Thanks,

Gordon Dickens