I only set this up for one domain under my ISPConfig, so you'll likely have to modify this to implement MailMan for all of your hosted domains.
Here's the rub with Debian. Debian's developer installs MailMan into /usr/lib/cgi-bin. Due to ISPConfig's virtual domain configuration, ISPConfig-created domains do not "see" Debian's main cgi-bin subdirectory.
What I did was to simply edit /etc/apache2/vhosts/Vhosts_ispconfig.conf (note I'm using Apache2) and make this change:
#ScriptAlias /cgi-bin/ /home/www/web1/cgi-bin/
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
and then restarted Apache. Note: this "breaks" the default ISPConfig cgi-bin for this domain.
Myself, I like using the command-line "newlist" command to create a mailing list. So I created a new mailing list, and added the list's aliases to /etc/aliases like the script tells you to. I then, of course, ran "newaliases".
From that point, I can access MailMan "normally", e.g. http://mydomain.org/cgi-bin/mailman/listinfo/
or whatever URL.
There is no doubt
that this is a crude fix. I don't use MailMan much, so it's a low priority hack just to get it working.
If you do actually put some effort into getting this working in a more integrated or comprehensive fashion, please let us all know...