如何使用EWS导出.ics文件中的所有约会

我正在使用EWS来管理Exchange Server电子邮件帐户的操作。如何导出.ics文件中日历的所有约会？我试着跟随。

string iCalFileName = Path.Combine(Path.GetTempPath(), "appointments.ics");
foreach (Appointment appointment in service.FindItems(WellKnownFolderName.Calendar, new ItemView(int.MaxValue)))
{
    appointment.Load();
    using (FileStream fs = new FileStream(iCalFileName, FileMode.Create, FileAccess.Write))
    {
        using (StreamWriter s = new StreamWriter(fs))
        {
            s.WriteLine(appointment.MimeContent.Content);//error must load property before using it
        }
    }
}

有人能告诉我我这里缺了什么吗？