如何使用 SmtpClient.SendAsync 發送帶有附件的電子郵件？

我正在通過 ASP.NET MVC 使用服務組件。我想以非同步方式發送電子郵件，讓使用者無需等待發送就可以做其他事情。

當我發送沒有附件的消息時，它工作正常。當我發送帶有至少一個記憶體附件的消息時，它會失敗。

所以，我想知道是否可以使用帶有記憶體附件的非同步方法。

這是發送方法

   public static void Send() {

       MailMessage message = new MailMessage("from@foo.com", "too@foo.com");
       using (MemoryStream stream = new MemoryStream(new byte[64000])) {
           Attachment attachment = new Attachment(stream, "my attachment");
           message.Attachments.Add(attachment);
           message.Body = "This is an async test.";

           SmtpClient smtp = new SmtpClient("localhost");
           smtp.Credentials = new NetworkCredential("foo", "bar");
           smtp.SendAsync(message, null);
       }
   }

這是我目前的錯誤

System.Net.Mail.SmtpException: Failure sending mail.
---> System.NotSupportedException: Stream does not support reading.
  at System.Net.Mime.MimeBasePart.EndSend(IAsyncResult asyncResult)
  at System.Net.Mail.Message.EndSend(IAsyncResult asyncResult)
  at System.Net.Mail.SmtpClient.SendMessageCallback(IAsyncResult result)
  --- End of inner exception stack trace ---

---

解決方案

   public static void Send()
   {

           MailMessage message = new MailMessage("from@foo.com", "to@foo.com");
           MemoryStream stream = new MemoryStream(new byte[64000]);
           Attachment attachment = new Attachment(stream, "my attachment");
           message.Attachments.Add(attachment);
           message.Body = "This is an async test.";
           SmtpClient smtp = new SmtpClient("localhost");
           //smtp.Credentials = new NetworkCredential("login", "password");

           smtp.SendCompleted += delegate(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
           {
                   if (e.Error != null)
                   {
                           System.Diagnostics.Trace.TraceError(e.Error.ToString());

                   }
                   MailMessage userMessage = e.UserState as MailMessage;
                   if (userMessage != null)
                   {
                           userMessage.Dispose();
                   }
           };

           smtp.SendAsync(message, message);
   }

不要在這裡使用“使用”。您在呼叫 SendAsync 後立即銷毀記憶體流，例如可能在 SMTP 讀取它之前（因為它是非同步的）。在回調中銷毀您的流。

引用自：https://stackoverflow.com/questions/279953