This is very off-topic but I'll mention it because you can install the whole server and be running faster than you can do the research to find something else. Look at http://www.e-smith.org. They have a modified Redhat distribution that is an 'office-in-a-box' and includes webmail access along with most of the other services you might want, all managed through a web interface. If you go to www.e-smith.com instead, you will find the commercial, supported service, but the .org site has a free iso image download and pretty good documentation on how to customize their template-driven configuration. The webmail program happens to be imp, using php and it currently doesn't have a way to authenticate against LDAP, although an LDAP directory is automatically updated as you add users.
Les Mikesell [EMAIL PROTECTED]