[exim] How to get the local MX? (And domain?)

Another question related to my routing experiments:

Is there a simple and direct way to obtain the MX for the local domain?
I mean the domain/network the host running Exim is connected to, not the
domain of the address(es) associated with a message. Also, how do I know
what domain that is in the first place? Is there a variable containing
the host's FQDN initial part removed, or similar.

- Toralf