[Exim] MX based routing, sort of

Hi,

I have what is probably a fairly unique situation and need some
advice/assistance. ISP connectivity is heavily restricted in Zimbabwe by
government regulations and as a result, all of the providers have to buy
at least outbound connectivity via TelOne (the national carrier).
Currently, TelOne has stuffed the routing to South Africa and as a
result we are routing all .za domains via a server based in the US. This
works well, except for domains that are based in South Africa that do
not have a .za domain name. What I am looking for is a solution (other
ideas are welcomed) that does something like this;

MX lookup for domain, if domain has a .za MX record, then route out via
an alternate smarthost. I know this will not solve the problem totally,
but it should help things along.

This probably sounds crazy to most of you, but the last time TelOne
stuffed up the routing, it took several weeks for them to fix it.


Thanks


Clint Sim