If you are using HTML (HTML: The standard markup language used for documents on the World Wide Web. HTML uses tags to indicate how Web browsers should display page elements such as text and graphics and how to respond to user actions.) format for your e-mail messages, you can reduce the size of the messages by sending them as filtered HTML (filtered HTML: Saving in the Web Page, Filtered format removes Microsoft Office-specific tags. If you save in filtered HTML and then reopen the file in Office programs, text and general appearance will be preserved, but some features may work differently.).
This option is not recommended when you plan to make major changes to your content later in Microsoft Word.