This chapter presents some basic Unix and email concepts that you need in order to follow explanations and examples presented later in the book. If you are already familiar with email administration, you can safely skip the material here and move on to the next chapter. This chapter does not give a systematic or comprehensive overview of either email or Unix administration. There is already an enormous amount of information available on both topics. This chapter simply presents an assortment of items that are referred to later in the book, with the expectation that readers already understand them.