The response returned from the server.
This property will be populated after a response is received from the server. If a receipt was requested this property will contain the receipt; otherwise this property will contain at least a small bit of HTML describing whether or not the transmission succeeded.
In case the receipt was signed, ResponseContent will contain the unsigned receipt, together with its MIME headers.
Note that if a signature was requested but an unsigned receipt is received the adapter will throw an exception.
This property is not available in the Receiver.