Question

I had configure smpt mail for my site and it’s work when I tried to send one single email but I have following error when I want to send it to more people, In addition I use SendAsyn method.

When I Send all Emails using LOOP

Syntax error, command unrecognized. The server response was:
at System.Net.Mail.SmtpConnection.ConnectAndHandshakeAsyncResult.End(IAsyncResult result)

at System.Net.Mail.SmtpClient.ConnectCallback(IAsyncResult result)

---

When I Add All Emails to BCC

Service not available, closing transmission channel.
The server response was: Too many bad commands, closing transmission channel
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpTransport.EndSendMail(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result

what is the solution for that ?

Answer 1

I have a similar situation whereby l am sending multiple emails and not waiting for one to finish before sending another.

What l did was initiate a new SMTPClient for every mail to be sent and send asynchronously. Like this:

        private void SendMailAsync(string ids, MailMessage mail)
    {
        SmtpClient client = null;

        try
        {
            client = new SmtpClient(ConfigurationManager.AppSettings["MailServer"], Convert.ToInt32(ConfigurationManager.AppSettings["MailPort"]));

            string userState = "MailQueueID_" + ids;

            client.SendCompleted += (sender, e) =>
            {
                // Get the unique identifier for this asynchronous operation
                String token = (string)e.UserState;
                DateTime now = DateTime.Now;
                try
                {
                    if (e.Cancelled)
                    {
                        LogError(new Exception(token + " - Callback cancelled"));
                        return;
                    }
                    if (e.Error != null)
                    {
                        LogError(e.Error);
                    }
                    else
                    {
                        logWriter.WriteToLog(this.jobSite + " - " + token + " (Email sent)");
                        try
                        {
                            int updated = UpdateMailQueue(token, now);
                            if (updated > 0)
                            {
                                // Update your log
                            }
                        }
                        catch (SqlException sqlEx)
                        {
                            LogError(sqlEx);
                        }
                    }
                }
                catch (ArgumentNullException argument)
                {
                    LogError(argument);
                }
                finally
                {
                    client.SendCompleted -= client_SendCompleted;
                    client.Dispose();
                    mail.Dispose();

                    // Delete the attachment if any, attached to this email
                    DeleteZipFile(token);

                    counter--;

                }
            };
            client.SendAsync(mail, userState);
            counter++;
        }
        catch (ArgumentOutOfRangeException argOutOfRange)
        {
            LogError(argOutOfRange);
        }
        catch (ConfigurationErrorsException configErrors)
        {
            LogError(configErrors);
        }
        catch (ArgumentNullException argNull)
        {
            LogError(argNull);
        }
        catch (ObjectDisposedException objDisposed)
        {
            LogError(objDisposed);
        }
        catch (InvalidOperationException invalidOperation)
        {
            LogError(invalidOperation);
        }
        catch (SmtpFailedRecipientsException failedRecipients)
        {
            LogError(failedRecipients);
        }
        catch (SmtpFailedRecipientException failedRecipient)
        {
            LogError(failedRecipient);
        }
        catch (SmtpException smtp)
        {
            LogError(smtp);
        }
    }

The error was caught in the SendCompletedEvent Handler.

Of course the error appeared for only one email while the other 7 went thru to different mail boxes both before and after it in the same run. What caused the error, l still don’t know.

When l ran my program again, it picked up the mail that was not sent and sent it off successfully.

Hope this helps others cos l realise that the question was posted more than 15 months ago.