This article outlines the database structure for the MMv4 em_attachment database table.

• template_id
  System ID of the specific email template associated with the Digital Object (attachment) for the email.
  int(10) | unsigned | indexed
  
• digobj_id
  System ID of the digital object in which is associated to the Email template. The digital object is the file attached to the email, if any.
  int(10) | unsigned | indexed