Ms Exchange Server Webservices中的From属性为空值

除了From属性返回为空白之外，此代码正常工作。再多的PropertySets似乎也无法解决这个问题。有人知道我哪里做错了吗?

Folder inbox = Folder.Bind(service, WellKnownFolderName.Inbox);
SearchFilter.SearchFilterCollection sfc = new SearchFilter.SearchFilterCollection(LogicalOperator.Or);
sfc.Add(new SearchFilter.IsEqualTo(EmailMessageSchema.IsRead, true));
ItemView view = new ItemView(1000);
view.PropertySet = new PropertySet(BasePropertySet.FirstClassProperties);
FindItemsResults<Item> findResults = service.FindItems(WellKnownFolderName.Inbox, sfc, view);

foreach (EmailMessage i in findResults)
{
  Console.WriteLine("Received: " + i.DateTimeReceived.ToString() + " From: " + i.From + " Subject: " + i.Subject);
}