After moving a client into another group, the client cannot create anything. So this is how I got the error: - Go to the tab Client -> Add Client - So far, everything is ok, the client can login and create sites and all the other stuff - I noticed, that a new group with the same login-name is created automatically - Go back to the CP as admin - System -> Edit User - Change default group an choose another group with the checkboxes. Unselect the automatically created group - Login as this client - The client cannot create anything, you always get the errors like "The max. number of email domains for your account is reached." Any idea what's causing the problem here? Also, I am a bit confused about the terms Client and User. Is it true that when one creates a Client, a User is also created? And what's the idea behind creating a non-admin User without creating a Client? Maybe I just have to wait until the documentation is ready for ISPConfig3.