[exim] Block spoofed unauthenticated spam mail

Hello,

I'm running exim on a cPanel server and I need to block all
unauthenticated mail (sent from mail() function of php) only when the
sender is setting up a from address with an external domain (not the
local main domain)

There is a way to do this with exim rules? If yes, can you tell me the
rules that I need to put into exim configuration?

Thanks a lot