When I installed ISPC on my colocated Mac mini in November, I wanted to check out a few different webmail clients. I saw that Uebimiau was the only one supported as an install into ISPC, but I honestly don't like it too much.
I ended up choosing what I was already familiar with, SquirrelMail. Then I was faced with the issue of getting it to be easily accessible to the customer. I ended up creating a server-wide alias in my apache2.conf file similar to the one I made for mailman.
Alias /webmail/ "/pathto/webmail/"
Alias /webmail "/pathto/webmail/"
will always work for whatever my clients' domain is.