ISPConfig3 creates the desired e-mail domain twice (on master server AND on the selected Slave)
ISPConfig3 creates the needed e-mail domain in /etc/vmail on the Master server in /etc/vmail AND on the selected slave server as well. (Double). This is very bad, the e-mail domain should only be created within /etc/vmail on the SELECTED server! For more information have a look at this thread: http://www.howtoforge.com/forums/showthread.php?t=46712