Disable iCloud using other SMTP servers

Since iOS 9 people I send messages to often get mail from one of my other email-addresses instead of the me.com email address I sent the message with.

I iOS mail settings I read that iCloud will use all other configured SMTP-servers to send mail via when iCloud is unavailable.

So it seems this is happening. And I don't want that to happen.

How can I prevent or disable this 'feature'?

Thanks for any suggestions.

- -

Marc