Last week i encoutered two typical issues.
one of them is about OUTLOOK. Our email system (based on Hosted Messaging and Collaboration 4.5 ---HMC4.5) was migrated  from an old IDC that hosted a legency HMC version.The primary procedure of migration is below:
1. Change MX record  to new IDC ip address that used to email service.Once changed the record, email will be relay to new IDC system---HMC4.5 that provids EXCHANGE 2007 to act as email server role.But previous emails sitll exist in old email storage that located OLD IDC untill we move all email storage  to new system.
2. export email storage to .pst file and copy these .pst file to new IDC server.
3. import .pst file for each exchange user.
Every step was been proceeded successfully.But there comes a trouble.
     when colleagues send mail with MS OUTLOOK 2003/2007 failed. The error prompted that recipients  unknow.

solution: edit outlook.nk2 .the file default path is: C:\Documents and Settings\%username%\Application Data\Microsoft\Outlook. need to delete some legency record.  use nk2view can read the file and you will find the incorrect content.

other issue is when i RDP to a dell poweredge 2950 that runing a windows server 2008 with Hyper-v ROLE. It display a error :Remote Desktop Disconnected Because of an error in data encryption, this session will end.  Please try connecting to the remote computer again.
  I try to restart terminal service firstly . After that, i try to RDP to the server ,it is ok. But it was been interrupted suddenly.
   In order to fix the RDC disconnection issues you need to disable the IPv4 Large Send Offload setting in the NIC's properties.