We can distinguish between two types of evil: natural evil and moral evil.

Natural evil is that which just happens as a result of natural processes. When the owl hunts and kills a rabbit, the death of the rabbit is a natural evil, but we can say that it is necessary, because the owls has to eat rabbit in order to live. Some bad things kind of just happen because that's how causality works.

Moral evil is deliberate wrongdoing by people. When we talk about evil, this is what we usually think about. Moral evil is never necessary, and we should always reject claims of "necessary evil" in the moral sphere.