Develop Reference

C# smtpfailedrecipientsexception; How to exit function if this happens

So here is my code which is used to send emails from Unity using a C# script:
public void SendMail() // Mail send function
{
string emailAddress; // variable to store user inputted email
emailAddress = emailInput.text; // variable becomes the email the user types in
mail.From = new MailAddress("hiddenfornow");
mail.To.Add(emailAddress);
SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
smtpServer.Port = 587;
mail.Subject = "Test Subject" + currentDate;
mail.IsBodyHtml = true; // allows for html
mail.Body = "Testing testing";
smtpServer.Credentials = new System.Net.NetworkCredential("hiddenfornow", "hiddenfornow") as ICredentialsByHost;
smtpServer.EnableSsl = true;
SceneManager.LoadScene("TestScene"); // reloads the scene after user clicks button
ServicePointManager.ServerCertificateValidationCallback =
delegate (object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
{ return true; };
smtpServer.Send(mail);
Debug.Log("success");
}
This code is working fine to send emails. However, if i enter an incorrect email i will recieve an "smtpfailedrecipientsexception" message.
After this, even entering a correct email address will not work. The smtpfailedrecipientsexception will continue to occur unless you type it correct the first time.
I would like to add some kind of If statement such as this which i've written in pseudocode:
If smtpserver.send(mail)returns smtp error
{
Exit this function
}
else
{
success message
}
I am just not sure how to implement this.

Use exception handling approach to dealing with runtime exception :
try
{
if (smtpserver.send(mail))
return "successful";
}
catch (SmtpFailedRecipientException ex)
{
// log your error
return ex.StatusCode; // return status code as you will know actual error code
}
finally
{
mail.Dispose(); // Dispose your mailmessage as it will clears any stream associated with your mail message such as attachment
}
Available Status Codes

The SmtpClient uses pooling to reduce the overhead of creating new connections to the server. (see: https://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient(v=vs.110).aspx#Remarks)
My assumption is that the SmtpFailedRecientsException is putting the connection into a bad state, so you need to force the connection to close by disposing the client:
public void SendMail() // Mail send function
{
//your code...
SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
try {
//.... your code continues.....
smtpServer.Send(mail);
Debug.Log("success");
} catch (SmtpFailedRecipientsException) { //or, perhaps any Exception
smtpServer.Dispose();
throw; //rethrow the exception, assuming you're handling it in the calling code
}
}

For future reference, here is the code which worked:
Try
{
smtpServer.Send(mail); // Attempts to send the email
Debug.Log("success");
}
catch (SmtpFailedRecipientsException) // Catches send failure
{
mail.Dispose(); // ends the SMTP connection
SceneManager.LoadScene("SceneName"); //Reloads the scene to clear textboxes
}

How to understand C# SendAsync function?

When i program with C# to send a mail by batch,my code is like this:
public static bool Send(MailAddress Messagefrom,
string MessageTo,
string MessageSubject,
string MessageBody)
{
MailMessage message = new MailMessage();
message.From = Messagefrom;
message.To.Add(MessageTo);
message.Subject = MessageSubject;
message.Body = MessageBody;
message.BodyEncoding = System.Text.Encoding.UTF8;
//message.SubjectEncoding = Encoding.BigEndianUnicode;
message.IsBodyHtml = true;
message.Priority = MailPriority.High;
MailHelper mh = new MailHelper();
SmtpClient sc = mh.setSmtpClient("smtp.qq.com", 25);
sc.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);
try
{
sc.SendAsync(message, message);
}
catch (Exception e)
{
LogHelper.WriteLog("Main send failed....\t the detail info:" +
e.ToString());
return false;
}
return true;
}
This is a problem!When the first mail send failed(for example the mail address is null),the next mail can't be send!
Because i have so much mail wait to send,if this situation,how to fix it?For example the failed mail may still on this table and Administator to deal it by hand.
But this situation probably in Send function,Why this happen?

You have to catch errors in the foreach loop that calls your Send() function and log the errors somewhere:
foreach (var mail in mailsToSend)
{
try
{
// Call your send function
Send(...)
}
catch (Exception ex)
{
// Log the error somewhere (console, file, ...)
Console.WriteLine("Error sending mail {0}", mail);
}
}
This ensures that the application won't crash when one email fails to send and continue sending the other mails.
Also you should use Send() instead of SendAsync() in your Send() function. This is because the SendAsync function starts a new thread for sending the mail, while Send will stop your programs execution until the mail has been sent. One more reason you shouldn't use the SendAsync function is because according to microsoft only 1 mail can be send at a time. That means using the SendAsync function for more then 1 mail will cause it to throw an exception.

Send Email Async

This is what I've tried for sending email using the SendAsync() method. When passing the bool to send regular email it works fine. When sending with the SendAsync method no dice. Just looking for some tips if you see something wrong here. Thanks in advance.
private static void SendEmail(System.Net.Mail.MailMessage m, Boolean Async)
{
using (var smtpClient = new System.Net.Mail.SmtpClient(EmailList.SMTP_GOOGLE, 587))
{
smtpClient.EnableSsl = true;
smtpClient.UseDefaultCredentials = false;
smtpClient.Credentials = new NetworkCredential("email#domain.com","password");
smtpClient.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
smtpClient.Timeout = 3000000;
if (Async)
{
object userState = m;
smtpClient.SendCompleted += new SendCompletedEventHandler(Smtp_OnComplete);
try
{
smtpClient.SendAsync(m, userState);
}
catch (Exception ex)
{
//Logging
}
}
else
{
try
{
smtpClient.Send(m);
}
catch (Exception ex)
//Logging
}
}
}
}

Your using statement is disposing the SmtpClient before the asynchronous send finishes.
That won't work.
Instead, you can either use C# 5 await to wait for the async send to finish inside the using statement, or get rid of using entirely for async sends and dispose the SmtpClient in the completion event.

I just set up a simple console app to run the methods for testing
Because the email is being sent asynchronously, the console app will start the method to in a different thread and continue with its own execution. If it closes before the method to send the actual email completes, the email will fail to send because Visual Studio will kill that thread. Try adding the following line after your call to send the email to make the console app wait a few seconds:
System.Threading.Thread.Sleep(5000);
This should be more than long enough for the email method to send the email and finish before the console app closes and Visual Studio kills all processes. The code should work fine on a web server.

sleeping a new thread c#

so im trying to delay the sending of email from my program.
In order to keep the UI interactive, i started a new thread and called the email method in the thread. It works. It sends the emails. However i cant figure out how to sleep the thread.
Ive tried using Thread.sleep() in the actual email method, but it doesnt seem to work.
Thread oThread = new Thread(new ThreadStart(() => { sendEMailThroughOUTLOOK(recipientAddress, subjectLine, finalbody); }));
oThread.Start();
email method..
public void sendEMailThroughOUTLOOK(string recipient, string subject, string body)
{
Thread.Sleep(60000);
try
{
// Create the Outlook application.
Outlook.Application oApp = new Outlook.Application();
// Create a new mail item.
Outlook.MailItem oMsg = (Outlook.MailItem)oApp.CreateItem(Outlook.OlItemType.olMailItem);
// Set HTMLBody.
//add the body of the email
oMsg.Body = body;
oMsg.Subject = subject;
// Add a recipient.
Outlook.Recipients oRecips = (Outlook.Recipients)oMsg.Recipients;
// Change the recipient in the next line if necessary.
Outlook.Recipient oRecip = (Outlook.Recipient)oRecips.Add(recipient);
oRecip.Resolve();
// Send.
oMsg.Send();
// Clean up.
oRecip = null;
oRecips = null;
oMsg = null;
oApp = null;
}//end of try block
catch (Exception ex)
{
}//end of catch
//end of Email Method
}

There is nothing apparently wrong with the code you've posted. However, thread.Suspend() is a very old API = it has been deprecated/obsoleted since .NET 2.0, as it's not safe to do this.
The static method Thread.Sleep(N) most certainly suspends the calling thread for N milliseconds.
To clarify; calling Thread.Sleep suspends the calling thread, so in your example code, where you have;
public void sendEMailThroughOUTLOOK(string recipient, string subject, string body)
{
Thread.Sleep(60000);
...
}
The call to Thread.Sleep(60000) is suspending the thread which is executing the method sendEMailThroughOUTLOOK. And since you appear to be calling that method in it's own thread,as evidenced by;
Thread oThread = new Thread(new ThreadStart(() => { sendEMailThroughOUTLOOK(recipientAddress, subjectLine, finalbody); }));
oThread.Start();
the correct thread should be suspended.
There is no way to do something like this;
Thread t = new Thread();
t.Start();
t.Sleep(60000);
You can start, or kill a running thread, but not sleep/suspend it. As noted - this API was deprecated as it is not a safe way to implement thread synchronisation (see http://msdn.microsoft.com/en-us/library/system.threading.thread.suspend%28v=vs.71%29.aspx for an explanation of why this is not a good idea).

Since you are a bit new to programming I won't try to explain all the relevant details but I thought it was cool that you showed me a new trick with your sample so I wanted to help you out if I could.
This isn't the only way to code this but I can tell you this is a reasonable one. It uses a background worker component to keep the UI responsive while sending the email. Note the use of the background worker's provided events DoWork and RunWorkerCompleted. The setup for these events took place in the designer which is why I zipped the solution up for you so you could take a look at the whole thing (I did so with google Drive and this is my first attempt doing a public share - if the link opens for you like it does for me, you'll get a File menu from which you can select Download).
I created an inner private class and passed it to the background worker. I do this because I don't want to access the data in my UI components from code running in a different thread. This will not always cause a problem but I find it to be a good practice in general. Also, it makes it so if I want to refactor the code later it will be easier to take the lines from DoWork and put them somewhere else without any fuss.
On the more general area of multi threaded programming - it's a multi faceted subject and you don't need to get it all right away. This is my favorite tutorial (the book is great too).
using System;
using System.ComponentModel;
using System.Windows.Forms;
using Outlook = Microsoft.Office.Interop.Outlook;
namespace Emailer
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void SendButton_Click(object sender, EventArgs e)
{
this.sendEmailBackgroundWorker.RunWorkerAsync(new _Email
{
Recipient = this.recipientTextBox.Text,
Subject = this.subjectTextBox.Text,
Body = this.emailToSendTextBox.Text
});
}
private class _Email
{
public string Body { get; set; }
public string Subject { get; set; }
public string Recipient { get; set; }
}
private void sendEmailBackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
var email = (_Email)e.Argument;
try
{
Outlook.Application oApp = new Outlook.Application();
Outlook.MailItem oMsg = (Microsoft.Office.Interop.Outlook.MailItem)oApp.CreateItem(Outlook.OlItemType.olMailItem);
oMsg.Body = email.Body;
oMsg.Subject = email.Subject;
Outlook.Recipients oRecips = (Outlook.Recipients)oMsg.Recipients;
Outlook.Recipient oRecip = (Outlook.Recipient)oRecips.Add(email.Recipient);
oRecip.Resolve();
oMsg.Send();
oRecip = null;
oRecips = null;
oMsg = null;
oApp = null;
}
catch (Exception ex)
{
e.Result = ex;
}
e.Result = true;
}
private void sendEmailBackgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
string message;
if (e.Result is Exception)
message = "Error sending email: " + (e.Result as Exception).Message;
else if (e.Result is bool && (bool)e.Result)
message = "Email is sent";
else
throw new Exception("Internal Error: not expecting " + e.Result.GetType().FullName);
MessageBox.Show(message);
}
}
}

Asynchronously sending Emails in C#?

I'm developing an application where a user clicks/presses enter on a certain button in a window, the application does some checks and determines whether to send out a couple of emails or not, then show another window with a message.
My issue is, sending out the 2 emails slows the process noticeably, and for some (~8) seconds the first window looks frozen while it's doing the sending.
Is there any way I can have these emails sent on the background and display the next window right away?
Please don't limit your answer with "use X class" or "just use X method" as I am not all too familiarized with the language yet and some more information would be highly appreciated.
Thanks.

As of .NET 4.5 SmtpClient implements async awaitable method
SendMailAsync.
As a result, to send email asynchronously is as following:
public async Task SendEmail(string toEmailAddress, string emailSubject, string emailMessage)
{
var message = new MailMessage();
message.To.Add(toEmailAddress);
message.Subject = emailSubject;
message.Body = emailMessage;
using (var smtpClient = new SmtpClient())
{
await smtpClient.SendMailAsync(message);
}
}

As it's a small unit of work you should use ThreadPool.QueueUserWorkItem for the threading aspect of it. If you use the SmtpClient class to send your mail you could handle the SendCompleted event to give feedback to the user.
ThreadPool.QueueUserWorkItem(t =>
{
SmtpClient client = new SmtpClient("MyMailServer");
MailAddress from = new MailAddress("me#mydomain.com", "My Name", System.Text.Encoding.UTF8);
MailAddress to = new MailAddress("someone#theirdomain.com");
MailMessage message = new MailMessage(from, to);
message.Body = "The message I want to send.";
message.BodyEncoding = System.Text.Encoding.UTF8;
message.Subject = "The subject of the email";
message.SubjectEncoding = System.Text.Encoding.UTF8;
// Set the method that is called back when the send operation ends.
client.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);
// The userState can be any object that allows your callback
// method to identify this send operation.
// For this example, I am passing the message itself
client.SendAsync(message, message);
});
private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
{
// Get the message we sent
MailMessage msg = (MailMessage)e.UserState;
if (e.Cancelled)
{
// prompt user with "send cancelled" message
}
if (e.Error != null)
{
// prompt user with error message
}
else
{
// prompt user with message sent!
// as we have the message object we can also display who the message
// was sent to etc
}
// finally dispose of the message
if (msg != null)
msg.Dispose();
}
By creating a fresh SMTP client each time this will allow you to send out emails simultaneously.

It's not too complicated to simply send the message on a separate thread:
using System.Net.Mail;
Smtp.SendAsync(message);
Or if you want to construct the whole message on the separate thread instead of just sending it asynchronously:
using System.Threading;
using System.Net.Mail;
var sendMailThread = new Thread(() => {
var message=new MailMessage();
message.From="from e-mail";
message.To="to e-mail";
message.Subject="Message Subject";
message.Body="Message Body";
SmtpMail.SmtpServer="SMTP Server Address";
SmtpMail.Send(message);
});
sendMailThread.Start();

SmtpClient.SendAsync Method
Sample
using System;
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
using System.Threading;
using System.ComponentModel;
namespace Examples.SmptExamples.Async
{
public class SimpleAsynchronousExample
{
static bool mailSent = false;
private static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e)
{
// Get the unique identifier for this asynchronous operation.
String token = (string) e.UserState;
if (e.Cancelled)
{
Console.WriteLine("[{0}] Send canceled.", token);
}
if (e.Error != null)
{
Console.WriteLine("[{0}] {1}", token, e.Error.ToString());
} else
{
Console.WriteLine("Message sent.");
}
mailSent = true;
}
public static void Main(string[] args)
{
// Command line argument must the the SMTP host.
SmtpClient client = new SmtpClient(args[0]);
// Specify the e-mail sender.
// Create a mailing address that includes a UTF8 character
// in the display name.
MailAddress from = new MailAddress("jane#contoso.com",
"Jane " + (char)0xD8+ " Clayton",
System.Text.Encoding.UTF8);
// Set destinations for the e-mail message.
MailAddress to = new MailAddress("ben#contoso.com");
// Specify the message content.
MailMessage message = new MailMessage(from, to);
message.Body = "This is a test e-mail message sent by an application. ";
// Include some non-ASCII characters in body and subject.
string someArrows = new string(new char[] {'\u2190', '\u2191', '\u2192', '\u2193'});
message.Body += Environment.NewLine + someArrows;
message.BodyEncoding = System.Text.Encoding.UTF8;
message.Subject = "test message 1" + someArrows;
message.SubjectEncoding = System.Text.Encoding.UTF8;
// Set the method that is called back when the send operation ends.
client.SendCompleted += new
SendCompletedEventHandler(SendCompletedCallback);
// The userState can be any object that allows your callback
// method to identify this send operation.
// For this example, the userToken is a string constant.
string userState = "test message1";
client.SendAsync(message, userState);
Console.WriteLine("Sending message... press c to cancel mail. Press any other key to exit.");
string answer = Console.ReadLine();
// If the user canceled the send, and mail hasn't been sent yet,
// then cancel the pending operation.
if (answer.StartsWith("c") && mailSent == false)
{
client.SendAsyncCancel();
}
// Clean up.
message.Dispose();
Console.WriteLine("Goodbye.");
}
}
}

Just because this is a little vague...I will be brief...
There are a lot of ways to do asynchronous or parallel work in c#/.net etc.
The fastest way to do what you want is to use a background worker thread which will avoid locking up your UI.
A tip with background worker threads : you cannot directly update the UI from them (thread affinity and Marshalling is just something you learn to deal with...)
Another thing to consider...if you use the standard System.Net.Mail type stuff to send the emails...be careful how you craft your logic. If you isolate it all in some method and call it over and over, it will likely have to tear down and rebuild the connection to the mail server each time and the latency involved in authentication etc will still slow the whole thing down unnecessarily. Send multiple e-mails through a single open connection to the mail server when possible.

Here is a fire and forget approach together with async using .Net 4.5.2+:
BackgroundTaskRunner.FireAndForgetTaskAsync(async () =>
{
SmtpClient smtpClient = new SmtpClient(); // using configuration file settings
MailMessage message = new MailMessage(); // TODO: Initialize appropriately
await smtpClient.SendMailAsync(message);
});
where BackgroundTaskRunner is:
public static class BackgroundTaskRunner
{
public static void FireAndForgetTask(Action action)
{
HostingEnvironment.QueueBackgroundWorkItem(cancellationToken => // .Net 4.5.2+ required
{
try
{
action();
}
catch (Exception e)
{
// TODO: handle exception
}
});
}
/// <summary>
/// Using async
/// </summary>
public static void FireAndForgetTaskAsync(Func<Task> action)
{
HostingEnvironment.QueueBackgroundWorkItem(async cancellationToken => // .Net 4.5.2+ required
{
try
{
await action();
}
catch (Exception e)
{
// TODO: handle exception
}
});
}
}
Works like a charm on Azure App Services.

Try this:
var client = new System.Net.Mail.SmtpClient("smtp.server");
var message = new System.Net.Mail.MailMessage() { /* provide its properties */ };
client.SendAsync(message, null);

What you want to do is run the e-mail task on a separate thread so the main code can continue processing while the other thread does the e-mail work.
Here is a tutorial on how to do that:
Threading Tutorial C#

Use the SmtpClient class and use the method SendAsync in the System.Net.Mail namespace.

Using the Task Parallel Library in .NET 4.0, you can do:
Parllel.Invoke(() => { YourSendMailMethod(); });
Also, see cristina manu's blog post about Parallel.Invoke() vs. explicit task management.

i think this is the best way :
public async Task Send(string to, string subject, string body)
{
MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient("smtp.mail.yahoo.com");
mail.From = new MailAddress("yourEmail#email.com", "sender name");
mail.To.Add(to);
mail.Subject = subject;
mail.Body = body;
mail.IsBodyHtml = true;
SmtpServer.Port = 587;
SmtpServer.Credentials = new System.Net.NetworkCredential("yourEmail#email.com", "your key");
SmtpServer.EnableSsl = true;
await Task.Run(() =>
{
SmtpServer.SendAsync(mail, null);
});
}