When mapping a domain to your WordPress, you may not want to select every single post or page individually to appear for your mapped domain.
To enable your website to map all unmapped pages automatically, you can simply check this box at the bottom of the plugin settings:
This will have the effect that every post, page, and other custom post type will appear as part of your mapped domain, and the corresponding slug of that page will be displayed as well.
This feature is mainly a "time-saver", so you don't have to manually select every page for mapping.
When mapping multiple domains to your site, you'll be given the option to define a default domain for mapping of all unmapped pages.
The checkbox changes automatically to display another option:
Here's a closer look at the additional option to select the domain to server for all unmapped pages
When you're done changing these settings, always be sure to click "Save" at the bottom.