Domain tab

[tom123]

What's the meaning of that tab? A domain should be added from the DNS tab and then in Sites and Mail....

[ressel]

The purpose is that your clients only are allowed to use the domains you have assigned them in domains tab.
So with domains tab enabled, they can only use domains you assign, without they can create sites, and email domains so much they want, within their number of limit.

Does it make sense?

[tom123]

Yes, that make sense.
Thank you.