Previously I blogged about an issue I first encountered with the Windows 7 M3 build (the one that was released at PDC) and my hosted Exchange provider.
In short when running the M3 build and the public beta I was unable to authenticate to my hosted Exchange provider using my email address and password. Instead I had to find out the domain name and enter credentials in the format DOMAIN\username in order for outlook to connect to Exchange. This was a bit of a pain.
The good news is that the Windows 7 Release Candidate resolves this issue and I can now authenticate with my email address as I could under Windows Vista.