Android mail app with only company email access

Hello,

we are using Mobile Device Manager Plus MSP. Our goal is to get mobile devices that are secure with no unwanted app and no change of system settings. The devices have only company email access. The phones are company owned so no BYOD.
For us the Kiosk mode was a proper solution for this.

Now we have 2 problems with email.
Since Android 8 Gmail seams to be the default email-config-setup app. So if you push the active sync settings and MDM will setup the password it will always open Gmail.
How can we change this or is there a work around?

We don't want to use the Gmail App, because the accounts settings are "open". This means you can add other private mail accounts.
So the other question is, what are other (enterprise) Mail Apps than can be configured with only the company active sync server?

Maybe the Mail App will also solve the first question :)

Thank you.