I got exception when I try to connect to my SMTP server using MailKit SmtpClient. BUT my mails have been sent successfully if I use System.Net.Mail.SmtpClient with the same parameters!
The exception message: An error occurred while attempting to establish an SSL or TLS connection.
The inner exception message: The handshake failed due to an unexpected packet format.
Questions
Why does MailKit.Net.Smtp.SmtpClient throw exception but System.Net.Mail.SmtpClient doesn't? What is the difference between them?
How to fix it?
Code
Initialize the parameters required for mail sending:
var host = "myhost.com";
var port = 2525;
var from = "from#mydomain.com";
var to = "to#mydomain.com";
var username = "from#mydomain.com";
var password = "myPassword";
var enableSsl = true;
Sending mail using System.Net.Mail.SmtpClient:
var client = new System.Net.Mail.SmtpClient
{
Host = host,
Port = port,
EnableSsl = enableSsl,
Credentials = new NetworkCredential(username, password)
};
client.Send(from, to, "subject", "body"); // success.
But when I try to connect to the host using MailKit with the same host and port, I got the exception:
var mailKitClient = new MailKit.Net.Smtp.SmtpClient();
mailKitClient.Connect(host, port, enableSsl); // it throws the exception.
The problem is that you are connecting to a plain-text port and expecting SSL.
In MailKit, the true/false useSsl parameter is used to decide whether or not to connect in SSL mode or plain-text mode.
In System.Net.Mail, they don't support connecting in SSL mode, they only support upgrading a plain-text connection to SSL mode using the STARTTLS command once the connection has been established.
To overcome this, MailKit has a different Connect() method that takes an enum value SecureSocketOptions.
What you want is SecureSocketOptions.StartTls:
var mailKitClient = new MailKit.Net.Smtp.SmtpClient();
mailKitClient.Connect(host, port, SecureSOcketOptions.StartTls);
Related
In May 2022, Google no longer supports the "Allow less secure apps" feature. So , I enabled two step verification in gmail using my phone and generated an App Password (16 digit random string) and used it in my C# code, but getting this excepton
"Failure sending mail. System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed."
The emails are read but unable to send emails, Please assist.
//Send email to client...
SmtpClient objSmtpClient = new SmtpClient();
objSmtpClient.UseDefaultCredentials = false;
objSmtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
objSmtpClient.EnableSsl = true;
objSmtpClient.Port = 587;
Email objSendMail = new Email();
objSmtpClient.Host = "smtp.gmail.com";
objSmtpClient.Credentials = new NetworkCredential("example#gmail.com","MyAppPassword");
objSendMail.From = "example#gmail.com";
objSendMail.To = customerEmail;
objSendMail.Subject = "Test subject";
objSendMail.Body = "Test Body";
try
{
var isSendEmail = objSendMail.SendEmail(objSmtpClient);
}
catch (Exception ex)
{
AppLogger.LogError(ex.Message + Environment.NewLine + ex.ToString());
return false;
}
After configuring an apps password this works.
using (var client = new SmtpClient())
{
client.Connect("smtp.gmail.com", 465, true);
client.Authenticate("xxxx#gmail.com", "AppsPassword");
client.Send(message.GetMessage());
client.Disconnect(true);
}
Another option would be xoauth2
Definitelly, it seems to be related to your Google Email Account, specifically. I'm facing the same issue in one of my Google accounts, even after I setup Two Factor Authenticator and App Password, like Google instructions (once "access to less secure apps" was discontinued, since 2022-may-30). When I try to send an email, I receive the following error message:
Unable to read data from the transport connection: The connection was closed.
So, after a couple of tries without success, I decided to try with another Google Account, making the same setup (Two Factor Authenticator an App Password creation), and the same source code I was using did the work.
I have contact Google in the following address in order to try to solve this issue in my specific account in the following contact url:
https://support.google.com/accounts/contact/less_secure_apps
Having feedback I will post it here.
I am trying to connect to iCloud via SmtpClient
The settings I am using are as follows:
Server name: smtp.mail.me.com
SSL Required: Yes
If you see an error message when using SSL, try using TLS or STARTTLS instead.
Port: 587
SMTP Authentication Required: Yes - with relevant username and password
If I use SSL I get "Handshake failed due to unexpected packet format"
If I don't use SSL visual studio debugger hangs on connect.
I think the problem is I am not telling the SmtpClient to use tls but I cant find documentation on how to do this.
The code is as follows:
using (var client = new SmtpClient()) {
client.Timeout = 1000 * 20;
//client.Capabilities.
client.AuthenticationMechanisms.Remove ("XOAUTH2");
client.Connect("SMTP.mail.me.com", 587, false); //dies here
//client.Connect(servername, port, useSsl);
//can I set tls or starttls here??
client.Authenticate(username, password);
client.Send(FormatOptions.Default, message);
}
Am I able to set TLS or StartTLS manually. One thing I did try is the following but it did not seem to work
client.Connect(new Uri("smtp://" + servername + ":" + port + "/?starttls=true"));
Thanks for any help with this.
The Connect() method that you are using only allows enabling/disabling SSL-wrapped connections which is not the same thing as StartTLS.
Due to the confusion, I've implemented a separate Connect() method that makes this more obvious what is going on:
using (var client = new SmtpClient()) {
// Note: don't set a timeout unless you REALLY know what you are doing.
//client.Timeout = 1000 * 20;
client.Connect ("smtp.mail.me.com", 587, SecureSocketOptions.StartTls);
client.Authenticate (username, password);
client.Send (message);
}
Try that.
You can set your options to "SecureSocketOptions.Auto"
something like this
await client.ConnectAsync(mailService.Host, mailService.Port, SecureSocketOptions.Auto);
MailKit will automatically decide to use SSL or TLS.
According to MailKit Doc
Connect(string host,int port,bool useSsl,CancellationToken cancellationToken = null)
The useSsl argument only controls whether or not the client makes an SSL-wrapped connection. In other words, even if the useSsl parameter is false, SSL/TLS may still be used if the mail server supports the STARTTLS extension.
This worked for me over the SecureSocketOptions.Auto option mentioned previously:
client.Connect(host, port, SecureSocketOptions.None);
I'm using code below to send an email and it just doesn't work and gives an exception:
MailDefinition md = new MailDefinition();
md.IsBodyHtml = true;
md.From = EMAIL_FROM;
md.Subject = "لینک تغییر رمز";
MailMessage mm = md.CreateMailMessage(to, null, new System.Web.UI.Control());
string body = link;
mm.Body = body;
SmtpClient smtp = new SmtpClient();
smtp.UseDefaultCredentials = false;
smtp.Host = EMAIL_SMTP;
smtp.Port = EMAIL_PORT;
smtp.Credentials = new System.Net.NetworkCredential(EMAIL_FROM, EMAIL_PASSWORD);
smtp.Send(mm);
where sender username & password are checked and correct, port is 25 and smtp is mail.kawp.co.ir, on send function it throws an exception with the below error message
{"Unable to connect to the remote server"}
{"A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond xx.xxx.xx.xx:25"}
I'm using the same method and function for my other domains which are hosted on the same server and they are working fine. What possibly could be causing the problem here?
p.s: I also can't handshake with the mail.kawp.co.ir 25 via telnet
Thanks in advance
Changing port 25 to 587 fixed my problem because my isp is blocking port 25 to prevent spamming.
If you cannot perform the handshake with Telnet, then you're not going to get it to connect programmatically. From what it sounds like, the server isn't configured to accept SMTP messages. You'll need to get that enabled before you can get your code to work.
I was trying to send emails in my Asp.Net C# application using port 465 with host "smtp.gmail.com" but the whole application hangs (keeps loading). When debugging it's stuck at SmtpClient.Send(msg).
Regardless of the credentials specified, it doesn't throw any exceptions to catch or any timeout errors. I have to close or refresh the page to regain access to the page.
If I put port 587 instead then every thing works fine and the SmtpClient.Send responds and sends the email or returns a proper exception such as operation timeout or failure sending email based on the credentials.
I simplified the code below for demonstration:
var smtp = new SmtpClient
{
Host = "smtp.gmail.com",
Port = 465,
EnableSsl = true,
Timeout = 200, // or any value it doesn't solve the problem
DeliveryMethod = SmtpDeliveryMethod.Network,
UseDefaultCredentials = false,
Credentials = new NetworkCredential("name#gmail.com", "password")
};
var msg = new MailMessage("name#gmail.com", "name#gmail.com", "Any subject", "Any body");
smtp.Send(msg); // stuck here
smtp.Dispose(); // never reached
msg.Dispose();
I tried SendAsync and reduced the timeout interval but this did not solve the problem. I think the problem is that smtp.gmail.com was reached but did not respond properly to port 465 and that's why the method was stuck.
I need to avoid such behavior since my application allows dynamic settings of the smtp server details and I don't want the whole application to hang in case of wrong details were entered.
Thank you,
Found this answer in case anyone gets here
SmtpClient Timeout doesn't work
Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
IAsyncResult result = socket.BeginConnect("192.168.1.180", 25, null, null);
// Two second timeout
bool success = result.AsyncWaitHandle.WaitOne(2000, true);
if (!success) {
socket.Close();
throw new ApplicationException("Failed to connect server.");
}
Wrap your SmptClient in a using statement, to ensure that Dispose is called.
I'm not sure if this is the cause or your problem or not, but I was having the same issues (sent correctly the 1st time, and often fails afterwards) at this has rectified it for me.
I'm trying to connect to a exchange server using OpenPop library and when I try to connect it says "Server is not available", this is my code:
Pop3Client Client = new Pop3Client();
Client.Connect("srv", 25, false);
Client.Authenticate("usr", "pass");
Can you show my what did I do wrong?
Thanks
If you authenticate with username and password you need to pass AuthenticationMethod.UsernameAndPassword to Authenticate:
using(var client = New OpenPop.Pop3.Pop3Client())
{
// Connect to the server
client.Connect(Pop3Server, Pop3Port, false);
// Authenticate towards the server
client.Authenticate("usr", "pass", OpenPop.Pop3.AuthenticationMethod.UsernameAndPassword);
// Get the number of messages in the inbox
int messageCount = client.GetMessageCount();
}
Note that I've used using-statement which is always recommend when an onject implements IDisposable.
Is "srv" a valid hostname? Try to ping the hostname in commandline.
And port 25 is usually the port for sending e-mails.
I would recommend verifying the port also.
The port is wrong.
Kindly use the following ports for POP3: port 110 or port 995 for Secure SSL.
Also kindly check that 'srv' is a valid hostname which I think is wrong as well.