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

Question

Hi,

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

I have tried your function and it works even for email with in memory attachments. But here are some remarks:

• What type of attachments did you try to send ? Exe ?
• Are both sender and receiver on the same email server ?
• You should “catch” exception and not just swallow it, than you will get more info about your problem.

• What does the exception says ?

• Does it work whan you use Send instead of SendAsync ? You are using 'using' clause and closing Stream before email is sent.

Here is good text about this topic:

Sending Mail in .NET 2.0

Answer 2

This works for me:

public void SendFile(String fromAddress, String toAddress, String fileName, String messageBody)
    {
        try
        {
            SmtpClient smtpClient = new SmtpClient("localhost", 2525);
            MailMessage message = new MailMessage();

            message.IsBodyHtml = false;
            message.BodyEncoding = Encoding.Default;

            using (FileStream fileStream = File.OpenRead(fileName))
            {

                MailAddress messageTo = new MailAddress(toAddress);
                message.To.Add(messageTo);

                MailAddress messageFrom = new MailAddress(fromAddress);
                message.From = messageFrom;

                message.Body = messageBody;

                Attachment messageAttachment = new Attachment(fileStream, Path.GetFileName(fileName));
                message.Attachments.Add(messageAttachment);
            }

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

            smtpClient.SendAsync(message, null);
        }
        catch (SmtpException smtpEx)
        {
            System.Diagnostics.Trace.TraceError(smtpEx.ToString());
        }
    }

Answer 3

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.