This is one of the many reasons I shy away from custom themes nowadays. The branding system is powerful enough to meet most needs for customizing the appearance of the cPanel interface and will gracefully adapt to new features as they are introduced - unlike custom themes which never inherit new functionality or UI improvements automatically.
If you wish to stick with the theme route instead of moving over to styles, I recommend copying the x3 theme completely and customize that to ensure you have all the latest improvements. I have a clone of the x3 theme on my test server and it displays the Email Import feature.
If your staff wants to migrate from using Themes to using Styles for customizing the appearance of cPanel, let me know and I'll be glad to assist.
Anyone wanting assistance with better understanding the advanced functionality of our Branding Editor and how it can meet your advanced UI customization needs, is welcome to email
sales@cpanel.net