If you've received a long email or are writing an email, you can split the email vertically into two sections so you do not have to scroll that much to refer to different parts of the email. [1
To share the e-mail, click in the Reading Pane or double-click the e-mail to open it, and then click Ctrl + Alt + S. This will create a horizontal divider in the middle of the Mail is displayed with a separate scroll bar in each area.
Now you can reference or compare different parts of the mail in the same window. To remove the split, double-click the separator bar.
This is a small but surprisingly useful feature.