MESSAGING_EMAIL_CACHE_GET_INDEX Messaging Endpoint
  /rpc/messaging/?method=MESSAGING_EMAIL_CACHE_GET_INDEX  
  Used for large email accounts when you are doing partial retrieves. Returns the index on the email server of a particular email that has been cached.  
  PARAMETERS TYPE NOTES
  Id Numeric  
  RETURN  
  Index Index of the email. Returns -1 if the email has been deleted off the server
  Count Total number of emails
  Message