Is iphone Mail app safe to use?

Personally I trust them, but not too much (you should never trust anything or anyone 100%).

As I said,

All companies like this want is, more money.

I trust Apple with my data but, not all of it. For example, I am moving slowly over to Proton Mail and Tutanota for my email. I also give just enough data to use their services.

Even though I trust Apple to some extent with my data, they are still big tech and by giving them my attention I am supporting big tech, which is not good. This is why I am slowly moving my life over to more privacy-focused alternatives, to get away from big tech companies and to regain my privacy.