In 3.0.1.1 I found a Bug. If user deletes email box, and create it again, the system cannot create the maildir. So it starts again, and again, and again... So kills MySql. What we need is check if the dir exist. If no then run maildirmake.
If you think you found a bug, please post it to the bugtracker so the developers can verify if its a bug or not: http://bugtracker.ispconfig.org
Tested it and it works fine on my systems. When a mailbox is deleted then all files are removed and when it is recreated it gets recreated without any problems.
