Makes sense, and after testing works like a charm. I did come up with another solution in searching, and it is found in this thread
Near the end of the first page of the thread, fastgrav explains that adding the following
add the following lines in /etc/apache2/conf.d/apache2-doc
Alias /webmail /usr/share/squirrelmail/
Options Indexes FollowSymlinks
Allow from all
and every virtual domain will have a www.virt-domain.com/webmail
and it works great without relying on having to worry too much about the settings per domain.