Authentication failed because the remote party has closed the transport stream

tuyen1644 21

I have application auto daily send email using smtpclient, it's still running OK before 1-Oct-2021. But from 1-Oct-2021, it send missing email, i use try catch to debug this and get exception below:

Please, give me a solution other than having to set up TLS1.2 in the application.
Thanks!

Timon Yang-MSFT 9,571 Reputation points

2021-10-12T06:25:20.17+00:00
@tuyen1644
Why don't you want to set TLS to 1.2?
This error is caused by this reason in many cases, just set it to solve the problem:

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

If it doesn't work for you, please provide a code example so that we can quickly reproduce your problem.
Vaishnav P 111 Reputation points

2021-10-12T13:57:14.513+00:00

Even I'm facing the same issue:

Error log

Failure Sending mail.
Authentication failed because the remote party has closed the transport stream

Not possible to connect to the mail server smpt.office365.com on port 587"

The email Encryption method used is TLS 1.2
PORT:587
SERVER: smpt.office365.com
SSL: yes
Kindly advise, as the issue occurs after 1st oct 2021
tuyen1644 21 Reputation points

2021-10-12T15:03:11.853+00:00

I use automatic mailing in many applications, so I can't update all of them, I want another solution that doesn't have to update the entire application in use. Thanks!
Jack J Jun 24,286 Reputation points Microsoft Vendor

2021-10-22T08:44:02.12+00:00

@tuyen1644 , As the Timon said, Could you provide a code example instead of picture in your question? It will be better for us to make a test.

tuyen1644 21

It' s my send mail function, you can run and check it. If you have any solution without having to edit this function, please suggest me. Thanks!!!

    public static bool SendEmail_Auto(string[] _email, string Subject, string body, string Link = "")
    {
        string EmailSender = "zzzz@xxx.yyy";
        string Pass ="xxxxxxx";
        try
        {
           MailMessage mail = new MailMessage();
            System.Net.Mail.SmtpClient SmtpServer = new System.Net.Mail.SmtpClient("smtp.office365.com");

            foreach (string to in _email)
            {
                mail.To.Add(to);
            }

            mail.From = new MailAddress(EmailSender, Title);
            mail.Subject = Subject;
            mail.Body = body;
            mail.IsBodyHtml = true;

            System.Net.Mail.Attachment attachment = null;
            if (Link != "")
            {
                attachment = new System.Net.Mail.Attachment(Link);
                mail.Attachments.Add(attachment); 
            }

            SmtpServer.Port = 587;
            SmtpServer.Credentials = new System.Net.NetworkCredential(EmailSender,Pass);
            SmtpServer.EnableSsl = true;
            SmtpServer.Send(mail);
        }
        catch (Exception ex)
        {
            return false;
        }
    }

Jack J Jun 24,286 Reputation points Microsoft Vendor

2021-10-27T02:39:17.357+00:00

@tuyen1644 , based on my test, the code you provided is correct, I can use it to send the email from hotmail.com to microsoft.com successfully. The question authentication-failed-because-the-remote-party-has.html is the same as your problem. You could have a look.

8 answers

KillboyPowerhead 1 Reputation point

2021-10-13T08:56:00.637+00:00

Same problem here.
Mail sending worked flawlessy unitl 1st oct. 2021 using SmtpClient in our applications targeting Framework 4.0. Unfortunately in the last days many of our customers using Office365 reported "Authentication failed because the remote party has closed the transport stream" error during some mail sending sessions.
It's not a constant error, after retrying a few times it works.
Our customers are mainly distributed throughout Italy, so i don't think the error to be related to physical connection issues.

We use "SmtpClient" like this, by assigning "SecurityProtocolType" casting 768 and 3072 to enum (since our platform require targeting Framework 4.0, we don't have Tls11 and Tls12 enum value):

ServicePointManager.SecurityProtocol =
SecurityProtocolType.Tls Or
DirectCast(768, SecurityProtocolType) Or
DirectCast(3072, SecurityProtocolType)
ServicePointManager.ServerCertificateValidationCallback = Function() True

ClientMail = New SmtpClient()
ClientMail.TargetName = "STARTTLS/smtp.office365.com"
ClientMail.EnableSsl = True
ClientMail.DeliveryMethod = SmtpDeliveryMethod.Network

It has always worked but now we are having a lot of troubles.
Any help?
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Evan Knutson 6 Reputation points

2021-10-14T16:36:24.213+00:00

I am also having the same issue. It's intermittent too. I also upgraded to TLS 1.2 by upgrading to .NET 4.5.2.
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Dario Graça 1 Reputation point

2021-10-27T15:19:50.597+00:00

Hello,

I was able to fix this by adding the following AppContext.SetSwitch to my code:
...
AppContext.SetSwitch("Switch.System.Net.DontEnableSystemDefaultTlsVersions", false);
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Ssl3;
...

Using FW 4.6.2
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