Styjun

I'm using NLog an target to send log to some emails using smtp.google.com:587 SMTP server. When I'm using standard System.Net.Mail.SmtpClient library it's working without any problems but when using MailKit it throw me error:

Error sending mail. Exception: >System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (10061): .No connection could be made because the target machine actively refused it .>[::ffff:173.194.76.108]:587

I added one solution with two console projects. One using MailKit and other System.Net.Mail. All settings parameters looks are the same but it doesn't work in MailKit:

using System;
using System.Diagnostics;
using MailKit.Net.Smtp;
using MailKit;
using MailKit.Security;
using MimeKit;

namespace SendMailKit

 class Program
 
 public static void Main(string[] args)
 
 Console.WriteLine("Create message");
 var message = new MimeMessage();
 message.From.Add(new MailboxAddress("GTS", "tfs.gettaxsolutions@gmail.com"));
 message.To.Add(new MailboxAddress("Me", "info@gettaxsolutions.com"));
 message.Subject = "Test mail";
 message.Body = new TextPart("plain")
 
 Text = @"Hello, This is the test"
 ;

 Console.WriteLine("Create SMTP client");
 using (var client = new SmtpClient())
 
 // For demo-purposes, accept all SSL certificates (in case the server supports STARTTLS)
 client.ServerCertificateValidationCallback = (s, c, h, e) => true;
 Console.WriteLine("Connect");
 **client.Connect("smtp.gmail.com", 587, true);**
 Console.WriteLine("Authenticate");
 client.Authenticate("tfs.gettaxsolutions", "*********");
 client.Connected += Client_Connected;
 client.Disconnected += Client_Disconnected;
 client.Authenticated += Client_Authenticated;
 client.MessageSent += Client_MessageSent;
 Console.WriteLine("Send Message");
 client.Send(message);
 Console.WriteLine("Disconnect");
 client.Disconnect(true);
 

 Console.ReadLine();
 

 private static void Client_MessageSent(object sender, MessageSentEventArgs e)
 
 Console.WriteLine("MessageSent");
 

 private static void Client_Authenticated(object sender, AuthenticatedEventArgs e)
 
 Console.WriteLine("Authenticated");
 

 private static void Client_Disconnected(object sender, DisconnectedEventArgs e)
 
 Console.WriteLine("Disconnected");
 

 private static void Client_Connected(object sender, ConnectedEventArgs e)
 
 Console.WriteLine("Connected");
 
 

And this throw the same exception like this one in NLog. the exception is in client.Connect("smtp.gmail.com", 587, true); So the problem is in the MailKit connect. In other project which using System.Net.Mail everything is working fine and the mail is sent successful. I'm starting them on same machine, same environment just change the startup point of console application to test (so the connectivity is not a problem):

using System;
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
using System.Threading;
using System.ComponentModel;
namespace SendSimpleMail

 public class Program
 
 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()
 
 // Command-line argument must be the SMTP host.
 SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
 client.EnableSsl = true;
 client.UseDefaultCredentials = false;
 client.Credentials = new NetworkCredential("tfs.gettaxsolutions", "***********");
 // Specify the email sender.
 // Create a mailing address that includes a UTF8 character
 // in the display name.
 MailAddress from = new MailAddress("tfs.gettaxsolutions@gmail.com", "GTS");
 // Set destinations for the email message.
 MailAddress to = new MailAddress("info@gettaxsolutions.com", "Me");
 // Specify the message content.
 MailMessage message = new MailMessage(from, to);
 message.Body = "This is a test email 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.");
 
 

I can't find what is the issue with MailKit. The settings looks like identical. Do you have some idea what can be a problem? Is it bug or have some problem in my settings?

MailKit have to send email successful

ASP.NET Core 2.2, MailKit 2.1.3

I just partly-solved a very similar problem merely a few minutes ago; what I learned may help you.

In the case I have, there was reliably working code for MailKit to send from application with target of NET Core 2.1.

Recently I updated all the Nuget packages, thinking it was good practice to do this. Then I later discovered that my working SMTP send code had suddenly stopped working and it was reporting identical error to what you have experienced.

With this situation I checked all kinds of problems with smtp server, firewall, etc., until I remembered the Nuget update, began experimenting and eventually downgraded MailKit to 2.0.0. The send code began working again once MailKit had the version downgrade.

I have not pinpointed the exact location and mechanism of failure but have developed some confidence that (in the case I have been working on) the MailKit version used is directly involved. For today it's restored to working on the MailKit 2.0.0 downgrade and there is more research to be done to take it beyond that status.

I changed the code of connect to this one:

client.ServerCertificateValidationCallback = (s, c, h, e) => true;
client.Connect("smtp.gmail.com", 587,
SecureSocketOptions.StartTlsWhenAvailable);

So it's clean that will use Tls when available. Certificate validation is turned off. It's working perfect in MailKit 2.0.7 but same code in 2.1.3 continue to throw the error in issue's description. Don't know why. May be have some bug in the all last versions(2.1.x)?

Part of the problem is that SMTP port 587 does not support SSL. You need to pass false as the useSsl argument.

Port 587 uses STARTTLS (which MailKit will automatically use if it can).

If you want more control, use the Connect[Async] methods that take a SecureSocketOptions enum value.

When using the Connect[Async] methods that take a boolean argument, true is the equivalent of SecureSocketOptions.SslOnCOnnect and false is the equivalent of SecureSOcketOptions.StartTlsWhenAvailable.

That said, however, the main part of the problem seems to be a bug in MailKit's newer Socket connection code. As of MailKit 2.1.x, MailKit began using Socket.BeginConnect (string host, int port, ...) instead of Socket.Connect (IPAddress address, int port) thereby allowing the underlying .NET implementation to resolve the host name into the appropriate IPAddress itself and to allow cancelability. Unfortunately, this seems to have broken things for some people (why?).

I have updated MailKit again to go back to resolving host names to a list of IP addresses (using Dns.GetHostAddresses[Async]) and looping over each IPAddress until it is able to successfully connect. This fix will be available in MailKit >= 2.1.4. Until then, you can install via the myget feed at https://www.myget.org/feed/mimekit/package/nuget/MailKit