EWS Blank Digital Subscription Letters After Upgrading from Exchange 2007 SP1 to Exchange 2013

Question

We are having a problem upgrading from Exchange 2007 Service Pack 1 (SP1) to Exchange 2013. We use ews to receive email from a specific folder. The code is as follows:

private List<Item> GetAllItems(string folderId)
    {
        Folder inbox = Folder.Bind(m_Exchange, folderId);

        List<Item> m_ListOfItems = new List<Item>();
        ItemView itemView = new ItemView(int.MaxValue);

        FindItemsResults<Item> items = inbox.FindItems(itemView);

        foreach (Item item in items)
        {
            item.Load();
            m_ListOfItems.Add(item);
        }

        return m_ListOfItems;
    }

Our problem with Exchange 2013 is when the email is digitally signed, in which case the email body is empty. For other emails, this is just fine for both plaintext / html email types. Also, this code works well even for digital signatures on Exchange 2007 Service Pack 1 (SP1).

Is anyone familiar with this problem?

Thank.