Q:

“List” property breaks retrieval of Send

The documentation on Send states I should be able to add a "List" property to learn from which list a user unsubscribed. However, when I use the List parameter, I receive "Error: The Request Property(s) List do not match with the fields of Send retrieve".
This appears to be an issue with the ExactTarget API. It would be great to have this corrected because currently I can only get all sends of a login without knowing which lists were effected.
Below, I have documented both a failed request with the "List" parameter, and a succeeding request where the only alteration is the removal of the "List" parameter. I have tried "List.ID" and other properties, to no avail.
Thank you for looking into this!

Service Reference URL: https://webservice.exacttarget.com/etframework.wsdl
var soapClient = CreateClient(settings.Username, settings.Password);

var retrieveRequest = new RetrieveRequest {ObjectType = "Send"};

retrieveRequest.Properties = new[] { "SentDate", "List" };

APIObject[] results;
String requestId;
soapClient.Retrieve(retrieveRequest, out requestId, out results);

*** Error: The Request Property(s) List do not match with the fields of Send retrieve

*** Now removing List from properties returns OK
var soapClient = CreateClient(settings.Username, settings.Password);

var retrieveRequest = new RetrieveRequest {ObjectType = "Send"};

retrieveRequest.Properties = new[] { "SentDate" };

APIObject[] results;
String requestId;
soapClient.Retrieve(retrieveRequest, out requestId, out results);

*** Returns OK
Yes this is similar to this question, but the ObjectTypes being requested are different. The answer to the stated question does NOT work for this ObjectType.

A:

Unfortunately, not all properties on an object are retrievable.  The best source for getting list of the retrievable objects is using the Describe method:
https://help.exacttarget.com/en/technical_library/web_service_guide/technical_articles/describing_a_subscriber/
For relationships like List to Send that are Many-to-Many, there is typically a junction object that represents that relationship.  For this scenario, the object is ListSend. 
https://help.exacttarget.com/en/technical_library/web_service_guide/technical_articles/retrieving_all_lists_for_a_send/

