I have just completed an exchange 2003-->2010 SP1 migration and everything seems to have gone fine aparts from a couple of issues, I have one user who is unable to connect to his mailbox either from his local client, or the terminal server (OWA works though).
The error that I get are
Unable to open your default e-mail folders. The microsoft exchange server computer is not available. Either there are network problems or the Microsoft Exchange server is down for maintenance.
I am getting this error from a terminal server with 20 users all working and connected to the exchange server fine, the issue is just with this 1 user.
I have checked the encryption settings on the server using Get-RpcClientAccess and EncryptionRequired is set to False (which I believe is the default for an SP1 installation anyway)
It is strange that I am just getting this for one user but from multiple clients.
I also have another user who has not been moved from the 2003 server who has lost permissions on people calendars (that have been moved to 2010) who they had access to before. Not sure if it is linked.