删除后，附件仍在导出的EmailMessage中

Question

为什么在删除附件后，附件仍然在导出的.eml文件中？

GetItemResponse i;
EmailMessage item = (EmailMessage)i.Item;

item.Attachments.Clear();
item.Update(ConflictResolutionMode.AlwaysOverwrite);

string filename = $"{item.Subject}.eml";

using (var fileStream = new FileStream($@"C:\{filename}", FileMode.Create))
{
    fileStream.Write(item.MimeContent.Content, 0, item.MimeContent.Content.Length);
}