Disallow sub-domains of the original domain to be used as mapped (primary) domain for sub-sites

Hello support,

I hope this finds you doing well this evening…

I have noticed this checkbox for some time…

Disallow sub-domains of the original domain to be used as mapped (primary) domain for sub-sites

This leads me to believe that if a subsite masks their domain with a custom URL; e.g. mysub.website.com is masked to myawesomesite.com, the site owner can then offer or allow for subsites on his or her site. e.g. nothersub.myawesomewebsite.com.

With this in mind, I have tried this but when attempting to add a subsite to the masked subsite domain, it still resolves to the primary site and attempts to setup a subsite on the primary domain instead of the masked subsite.

Now, I know this is somehow possible because I have (until recently prevented) seen bots setup spam sites and the base url looks like this:

spamsite.mysub.website.com where mysub.website.com is myaweseomwebsite.com and when I looked at spamsite.myawesomewebsite.com it resolved as expected.

So what am I missing or what needs to be done to allow for this? I’m also expecting that spamsite.mysub.website.com which is spamsite.myawesomewebsite.com can be masked to spamsitehacker.com if so desired…

Can you please let me know if I”m remotely understanding this correctly and if so what needs to be done to allow for this from the frontend of sites and not just to hackbots…

Thanks!