Dude What are you on about??
Dude What are you worried about??
What security issues did you fix?
The ISPconfig installer configures the mail server, and it is secure.
Tell me exactly what security holes there are in a default setup.
if you have to change things, install ISPconfig first, then make changes.
And by the way, no product manual is going to tell you what to do after you mess up the mailserver installation.