You can view emails in split screen mode on the ipAd

Double tap on an email in the inbox or in the email drafts screen to open the email into a new window.

When you are editing a new email, you can also select "New Window" in the action menu to open the email into a new window beside the main app window.
When you are editing an email in the split screen mode, you can view an email in the other screen and drag attachments to the new email or copy and paste text.

Use the "..." button in the top of the iPad screen to view all windows, add a new email in a new window or close the current window.