In PBU you can add a custom @domain address to the shortcuts above the keyboard when a guest shares through email. This is useful when for corporate events where many guests have the same email domain, e.g. @laphotoparty.com.
Note: You can also enable this feature when using PPU Kiosk on your Windows tablet. Check out the solution HERE for more details.
Open PBU settings and select the Misc. tab. Enter your custom @domain in the box labeled Custom Keyboard Email. Then click OK at the bottom.
Now when a guest clicks Email for their sharing option they will see the custom @domain as a shortcut above the keyboard on the right.
Congrats! You're all set with a new custom keyboard email.