one confusing thing about the intro demo

Hello, I watched the Virtualmin intro demo with interest - http://www.virtualmin.com/video-introduction.html

one thing that I did not see is how the Email/FTP user was linked to an actual Unix user account.

I.e., I saw how an email user was created, but I did not see how a physical user of the machine could make use of that email user.

However, given all of the excellent free support I have had with Webmin, I'm sure there is a good and simple answer and will go ahead and get Virtualmin Pro :)