Exim's configuration is very expressive. Being able to do complex things has the tradeoff of being able to get lost in the complex things you've done, that's a

Exim's configuration is very expressive. Being able to do complex things has the tradeoff of being able to get lost in the complex things you've done, that's a given. But I wouldn't call it complicated, not really. Expansions usually bite, but it had a REPL-like facility for getting them right since forever. The rest is pretty nice and clean DSL in my opinion.