When you scroll a large list of emails, a scrolling navigator will appear in the middle of the screen to assist you. This will allow you to tap (or drag) on a month or group of emails to quickly scroll to that position. For example, you can quickly go to May last year by tapping on the date in the navigator.
This makes it easier to navigate through large lists of emails.

You can also tap on the up and down arrow buttons in the list to jump to the top or bottom of the email list.

You can turn the scrolling navigator on or off in the app settings -'Email' section - 'Show email folder scroll navigator'