Passing info into an entityform?
Did you try the Prepopulate module? Entityforms just use Drupal Fields so I imagine it should work. You would then just define the values per field in the URL from your email.


  The Prepopulate module allows fields in most forms to be pre-populated
  from the $_REQUEST variable.
  
  For example, the following URL,
  
  http://www.example.com/node/add/blog?edit[title]=this is the title
  
  will automatically fill the Title field on a new blog post with the
  words "this is the title". Any field can be prepopulated this way,
  including taxonomy and CCK fields. You can prepopulate more than one
  field at a time as well. Prepopulate is excellent for creating
  bookmarklets. For examples on usage for all of these cases, please
  read the USAGE.txt file that comes with the module or you can read the
  online handbook page.