It's interesting that you should upload that diagram. I've been intimately involved with running a hosting business for years and have always struggled with demonstrating graphically to the clients how "email" works. It is in fact a huge subject and trying to simplify it into a schematic that I can understand is easy, and Xara is the perfect tool for doing so (for me). However, illustrating it so that a novice can understand it isn't at all simple. I can see a few holes in your diagrams, not necessarily because you have made mistakes, but because you have left things out. But there just isn't enough space on such a schematic to explain the fundamental difference between, for example, POP and IMAP, differences that would have a dramatic effect on the customer's experience of his email client. And then you throw Webmail into the melting pot and you have people crying into their tea.