Feature request: add values to DomainKeyUtil#getEnvironment()

[jak837]

Maybe in a future version there could be a way to add key/values to the map created in DomainKeyUtil#getEnvironment()?
This way developers can change DNS that is being used.
fx if a developer can add:
environment.put("java.naming.provider.url", "dns://8.8.8.8");
It use google dns for looking up the record.

Alternative a explicit dns api could be added to the library.

[bbottema]

I guess it makes sense to make the DNS host configurable. I would prefer to do that with explicit api, rather than a generic map.