Selectively update an email destination by DestinationId. A nonempty To array replaces To recipients; null or an empty To array preserves them. For Cc and Bcc, null preserves existing recipients and an empty array clears them. Omitting Cc or Bcc initializes an empty array and can therefore clear recipients. Nonempty Subject, Body, BodyFormat, CustomSenderName and CustomerSenderAddress replace their stored values; null or empty strings preserve them. Omitted BodyFormat defaults to TEXT, so send null to preserve the stored format. Output, naming, enabled and embedding settings are not changed by this operation.