When the conversation property isn't available (in Exchange 2003/2007), Outlook uses the Subject field. Outlook's POP, IMAP, Outlook Connector/EAS message transport and Exchange Server 2010/2013 add a conversation property to the message when messages arrive and uses this value to group messages by conversation. Unfortunately, you can't remove messages from conversations either. How can I tell Outlook this needs to be in it's own conversation thread? Somebody uses an e-mail in a particular conversation to start a new topic or refer to an existing topic that is unrelated to the current conversation.
