After some more searching, found a plugin vhost already installed with the package from ispconfig. This made the @mywebsite.com be entered in the login user space. This would have been great if the installation of the package would allow all site hosted through ispconfig reach squirrelmail.
In fact the only site that allows the squirrelmail through the actual installation of the package, is the ispconfig site https://www.mywebsite.com:81/squirrelmail
How do I fully take advantage of this package? I imagine I could make an alias of the directory squirrelmail, and inserted in each new site as they are created. Will this work?
I still get no emails in the account created, though I can send.