Copyright law stops other people from using and abusing your original work.
Email messages are creative works and therefore copyrighted.
You do not have to register this copyright - it exists automatically. If you are the author or maker of an original creative work, copyright law gives you the right to exclude others from using your work in certain ways. You should be able to control who makes copies, or creates a work derived from yours. Email messages, handwritten notes, books, computer programs and webpages are all creative works and they are all protected by copyright. Copyright exists automatically from the moment that a creative work is given tangible form - as in a webpage or email message.