[exim] need help with a filter

I swore I'd never do this, but I've gone through all the docs I can, and
haven't been able to find the answer anywhere, and I'm hoping you guys can
help me.

What I need is a way to check whether email that is being recieved for a
specific address, came from a specific host. If it did, to deliver it as
normal, if not reject it.

sounds simple, but for the life of me I can't seem to find anything that
tells me how to do it