Mail app "pop up" and steals keyboard/mouse focus

I have the Mail app set up to "pull" emails every 15 minutes from the servers.

If I leave Mail running as a background process, every time it does a check for mail it pops-up over all my running apps and steals focus.

This is really frustrating for me because if I am typing something in terminal or another app like Pages, Mail takes over the screen and takes all my keyboard inputs away from the process already in focus. I then have to click to close the mail app so I can get back to my other tasks.

How do I stop Mail from popping up and stealing the mouse and keyboard focus every time?

I am at the point of killing Mail and only opening the app when my iPad gives me a mail notification. I am also now looking to replace Mail as my main email app. I do not want to use mail "push" because its a battery drain and Mail "pops up" more frequently to steal focus.