If you changed anything, restore it to the way it was, NO modifications are needed to the /home/adminispconfig/web/squirrelmail/config/config.php file, everything works after installing the Squirrel Mail Plugin, then read the thread below:
After installing the plugin in ISPConfig read the thread below:
http://www.howtoforge.com/forums/sho...7668#post87668
KEY TO SOLUTION: You have to Configure Squirrel Mail As if it was a Regular E-Mail Client.
Jack