.net - How to send an email with attachments using SmtpClient.SendAsync?

Question

I am using a service component through ASP.NET MVC. I would like to send the email in a asynchronous way to let the user do other stuff without having to wait for the sending.

When I send a message without attachments it works fine. When I send a message with at least one in-memory attachment it fails.

So, I would like to know if it is possible to use an async method with in-memory attachments.

Here is the sending method

    public static void Send() {

        MailMessage message = new MailMessage("[email protected]", "[email protected]");
        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);
        }
    }

Here is my current error

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 ---

---

Solution

    public static void Send()
    {

            MailMessage message = new MailMessage("[email protected]", "[email protected]");
            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);
    }

Answer 1

Don't use "using" here. You are destroying the memory stream immediately after calling SendAsync, e.g. probably before SMTP gets to read it (since it's async). Destroy your stream in the callback.