[imp] Email client for many servers?

[Burton]

Hi,

I'm hosting a few websites and want to be able to
provide web based email access for each.  I want to
avoid having users install an email client on their
own servers.

So for example, I have site1.com and site2.com running
on the same server.  I'd like jim at site1.com and
bob at site2.com to be able to read and reply to email
from one installation.  

The email access for site1/site2.com could come from
site.com.  

Can imp/Horde do this?  Would it be tricky to pull
off?  I looked at Squirrelmail, but you only get to
specify one server.

Thanks!