You can use the Exchange 2010 Tracking Log Explorer to determine which user an email is being redirected from. This is useful when you need to find out how a user is receiving an email from a distribution group when they are not a member of that distribution group.
I have been trying to work out why emails were still being moved to user’s Junk Email folder in Outlook 2007 even though Junk Email Filtering was turned off by Group Policy. It turns out Exchange 2010 has it’s own Content Filtering which can move emails to the Junk Email folder regardless of your Outlook setting.
Part of the transition from Exchange 2003 to 2010 has involved getting our BES 5 server to work with the new server.
I’m using the transition method to upgrade from Exchange 2003 to Exchange 2010 for approximately 250 mailboxes with all roles on a single server. Here are a few notable points if you're perfoming the migration.