I have a client with SBS 2011 Standard fully patched. I have set up a 2nd accepted domain on their server with a single user mailbox that 3 users have full managed access to. However if one user opens / reads an email it is not synchronised to the other instances of the mailbox on other users Outlook 2010 clients. Similarly if a user then marks an email as Unread it does not update on the other Outlook client instances. This behaviour is not replicated on the other accepted domain.