Do you have an API?

Great question! We do have a fully functional API. Utilizing cPanel as our frontend, this is one of the many things that we gain without having to develop ourselves. Certainly as a small business we can't have every single thing developed in-house, and it's great to be able to rely on the cPanel developers to provide this.

First, you can reference the cPanel UAPI email functions here:
https://documentation.cpanel.net/display/SDK/UAPI+Modules+-+Email

Now you're probably thinking "That's great, but can you show me an example of how this functions in fully developed code?" Sure! Check out this open source PHP class available on GitHub:
https://github.com/N1ghteyes/cpanel-UAPI-php-class

You can see that their example script was for creating a MySQL database:
https://github.com/N1ghteyes/cpanel-UAPI-php-class/blob/master/examples/mysql.php

Obviously the MySQL database isn't relevant to our service, but you can take that and incorporate what you find here to figure out how to script the addition of an email account over API:
https://documentation.cpanel.net/display/SDK/UAPI+Functions+-+Email%3A%3Aadd_pop

Cool, right? The only thing that stands between you and a fully custom, white-labeled MXroute experience for your customers will be your knowledge, time, and commitment.