Abstract:

Outlook Anywhere may not work properly on a Windows Server 2008 machine with Exchange 2007.  The DSAccess RPC proxy listens on ports 6001 and 6002 on the IPv6 stack, and listens on ports 6001, 6002, and 6004 on IPv4.  The missing listener on port 6004 causes connectivity to fail.
A workaround exists and is documented which gets this working, regardless of where the RPC proxy is installed (on the Exchange box, or otherwise.)

Details:

If your RPC proxy is on 2008, but not on the same box as Exchange 2007, remove the IPv6 binding to force the proxy to communicate with Exchange on IPv4.

Otherwise, modify your host file, as per: http://weblog.bassq.nl/?p=79

• Comment out the line “:::1 localhost”
• Add the following two lines:
  <IPv4 address> <hostname of the computer>
  <IPv4 address> <FQDN of the computer>

So, for my server, I have:
10.0.0.5 servername
10.0.0.5 servername.subdomain.domain.com

To confirm functionality:

Open telnet to localhost 6004

Sources:
http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2975122&SiteID=17