Please note there are often problems when using old operating systems (like Windows XP) and/or old email clients (like Outlook 2003) when connecting to a Hosted Exchange mailbox. Also, not all the great features of Hosted Exchange are enabled when you are using an out-of-date email client like Outlook 2003.
Recently a change to Windows XP or Outlook created some issues for users running Outlook in combination with a Windows XP operating system and this has prevented them accessing their Hosted Exchange mailbox - if this has happened to you please follow these instructions:
Click "File" in the top left hand corner
Click "Account Settings"
Click "Account Settings" again in the drop down menu
Double Click on your email address in the window that pops up
Click on “More Settings”
Click on the “Connection” tab
Click on “Exchange Proxy Settings”
Put a tick on both boxes “On fast networks….” and “On slow networks…”
Click “Ok” and close all boxes.
There have been quite a few forums referring this to issue and this link is for one of the better ones: http://support.microsoft.com/kb/956531