Tangential fun fact:
Snake oil is a real thing, that actually helps with the some very specific problems. But it has to be made a specific way from a specific snake. We associate the term with scams because of the large number of scammers that advertised fake snake oils, or advertised it being useful for tons if things it wasn’t.
My point is, many of the most effective scams rely on something that has a kernel of truth.
I use mailbox.org personally. Disroot is probably fine.
If you’re worried about hacking, you can do some things to mitigate the damage that would cause. Download important old emails and delete them from the server, this is pretty easy to do in a desktop client (like thunderbird or outlook) where you’d just move them to a local folder. That way if someone gains access, or they sell to someone that processes the data, they won’t have the old emails (unless they for some reason retained a separate copy, which seems doubtful).