The email submit button is a standard button that has certain properties already set and a specialized Object palette. This object makes it easier for you to create buttons that users can click to return their form data by email. Because Adobe Reader does not save changes to PDF files, including form data, it is a good idea to include an email submit button on forms that users may fill in Adobe Reader.
After you add a button to the form design, you can edit the caption text, and you can manipulate the object’s properties in the Field tab of the Object palette. You can define these properties:
See also 

Overview of email submit buttons