解决方法
这里发布了一个更简单的解决方案：
Get body from Outlook email [Drag’n’Drop]
@H_404_8@Outlook.Application outlook = new Outlook.Application();
Outlook.Explorer oExplorer = outlook.ActiveExplorer();
Outlook.Selection oSelection = oExplorer.Selection;
foreach (object item in oSelection)
{
Outlook.MailItem mi = (Outlook.MailItem)item;
Console.WriteLine(mi.Body.ToString());
}
它使用Microsoft.Office.Interop.Outlook.dll. (它与NuGet同名)