I have installed RoundCube on a Linux host to provide free email server.
1. a new user sign up screen for the new new registration.
2. add Subuser functions:
a. A regular user (User A) is a normal registered email user of the domain
b. A subuser (User B) is not a normal registered email user. It is created by User A and Managed by User A
c. Build a mini admin panel for User A, with about 5 functions
Roundcube source code can be downloaded at:
[url removed, login to view]
Will provide a test site.