(add client request)
https://mandrillapp.com/api/docs/metadata.JSON.html#method=add
(delete client request)
https://mandrillapp.com/api/docs/metadata.JSON.html#method=delete
(list client request)
https://mandrillapp.com/api/docs/metadata.JSON.html#method=list
(update client request)
https://mandrillapp.com/api/docs/metadata.JSON.html#method=update