There s a great deal I had to leave out; after all, this book is about securing Exchange messaging systems, not a general treatise on securing Windows. Even within Exchange, I had to choose what could fit in the time and space allotted for the book. Accordingly, there s no coverage of security for real-time conferencing or migration security. Even though some sites will still be using the Exchange 2000 Server instant messaging service, or the Exchange 5.5 or Exchange 2000 Server chat services, in conjunction with Exchange Server 2003, those topics aren t covered either.