If you are using the default email client on your Galaxy S7 (the Email app), you can change the notification sound for new emails. To change email notification sound on Galaxy S7 (Edge), do as follows:
1. Open the Email app on your Galaxy S7 (You may find it under the Samsung folder and don't confuse it with the Gmail app)
2. Hit the More button on the top right of the screen, and go to the Email's Settings.
3. Scroll down to the General settings, and touch the Notifications option
4. Choose the account to you want to change the notification sound for
5. Now tap the Notification Sound option and on the opened list of sounds, select the notification sound for the Email app on your Samsung Galaxy 7 and Galaxy 7 Edge