If you have emails that were either created outside Workbooks (in Outlook or Google Mail for example) or you've received email in your Inbox that you want to store against the relevant record(s) in Workbooks, you can use the Dropbox functionality.
Put simply, the Dropbox is a special email address (different for each Workbooks user). When emails (up to 16MB each) are received by that address, Workbooks searches the database to find the right record(s) to store the email against. You can store the same email against many different records within Workbooks (up to a maximum of 500 per email). For example, you might want to store one email against not only a Person, but also against a Case that the Person has raised. This can be achieved easily by including Object References in the emails you forward to your Dropbox.