I didn't find any alternative yet. There are a lot of cloud based alternatives, but that's a privacy nightmare. eM Client looks promising, just came out of beta and works without a MITM cloud service.
I personally can’t imagine not using the native email app. It’s quite nice.
That may be what the person you replied to is referring to as well. It’s been a trend for a while that new email apps (either on Desktop or phone) use their own server in the middle with access to your credentials to do stuff like syncing and sending emails on a schedule.