anchor.diff:  |from |string or JSON  | Address _"from" : "deals@company.com"_ or JSON object composed of the "name" and "email" fields _"from" : { "name" : "My Company", "email" : "deals@company.com" }_ used to compose the email's "From" header| yes | Substitution syntax is supported. |
   |reply_to |string  |Email address used to compose the email's "Reply-To" header | no | Substitution syntax is supported. |
   |headers| JSON | JSON dictionary containing headers other than "Subject", "From", "To", and "Reply-To"  | no |See the Header Notes. |
  -|attachments| JSON | JSON array of attachments ( **Note:** SparkPost Elite only ) | no | For a full description, see the Attachment Attributes. |
  -|images| JSON | JSON array of inline images ( **Note:** SparkPost Elite only ) | no | For a full description, see the Image Attributes. |
   
   #### Header Notes
   
  
positive.code:           }
          }
  
  
  
  ## Retrieve [/transmissions/{id}]
  
negative.code: |open_tracking |boolean |Enable or disable open tracking | no - defaults to the setting at the transmission level | To override the default for a specific transmission, specify the _options.open_tracking_ field upon creation of the transmission. |
  |click_tracking |boolean |Enable or disable click tracking | no - defaults to the setting at the transmission level | To override the default for a specific transmission, specify the _options.click_tracking_ field upon creation of the transmission. |
  |transactional |boolean |Distinguish between transactional and non-transactional messages for unsubscribe and suppression purposes | no - defaults to the setting at the transmission level | To override the default for a specific transmission, specify the _options.transactional_ field upon creation of the transmission. |
  
  ## Error Attributes
  
  