Zog, I'm not sure why your mails are ending up there. All my mail goes to /var/vmail/usersmailboxesetc. You can read these mails from the root account using the command vi filename or cat filename. There are three directories with mail: cur, tmp and new.
Like you, I started off using other distributions but in the end switched over to debian using this tutorial:
Although other distros are supported it's worth bearing in mind that ISPconfig3 was developed on debian and this is what the developers are using, so when you ask for support, and you've used that guide, who ever is good enough to help knows exactly what your have in place already.