VSTO C# Outlook通过POST发送文件，只有在上传完成后，Outlook才会收到响应

using System;
using System.IO;
using System.Net;
using System.Windows.Forms;
using Outlook = Microsoft.Office.Interop.Outlook;

namespace OutlookAddIn
{
    public partial class ThisAddIn
    {
        private void ThisAddIn_Startup(object sender, EventArgs e)
        {
            // 在启动时执行必要的初始化操作
        }

        private void ThisAddIn_Shutdown(object sender, EventArgs e)
        {
            // 在关闭时执行清理操作
        }

        protected override Microsoft.Office.Core.IRibbonExtensibility CreateRibbonExtensibilityObject()
        {
            return new CustomRibbon();
        }
    }

    public class CustomRibbon : Microsoft.Office.Core.IRibbonExtensibility
    {
        public void UploadFile(Office.IRibbonControl control)
        {
            // 打开文件选择对话框
            OpenFileDialog openFileDialog = new OpenFileDialog();
            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                // 获取选择的文件路径
                string filePath = openFileDialog.FileName;

                // 创建Web请求
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://example.com/upload");
                request.Method = "POST";

                // 读取文件内容
                byte[] fileBytes = File.ReadAllBytes(filePath);

                // 将文件内容作为请求的一部分发送
                using (Stream requestStream = request.GetRequestStream())
                {
                    requestStream.Write(fileBytes, 0, fileBytes.Length);
                }

                // 获取服务器响应
                using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                {
                    // 处理响应
                    if (response.StatusCode == HttpStatusCode.OK)
                    {
                        // 上传成功
                        Outlook.MailItem mailItem = Globals.ThisAddIn.Application.ActiveInspector().CurrentItem as Outlook.MailItem;
                        if (mailItem != null)
                        {
                            mailItem.Body += "文件上传成功！";
                            mailItem.Save();
                        }
                    }
                    else
                    {
                        // 上传失败
                        MessageBox.Show("文件上传失败！");
                    }
                }
            }
        }

        #region IRibbonExtensibility 成员

        public string GetCustomUI(string ribbonID)
        {
            return Properties.Resources.Ribbon;
        }

        #endregion
    }
}