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 9,576 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 24,296 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 24,296 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

Andy David - MVP 142.2K Reputation points MVP

2021-10-12T13:58:07.23+00:00

Is MFA required for this account? If so, that is expected.
Please sign in to rate this answer.

1 person found this answer helpful.
Vaishnav P 111 Reputation points

2021-10-12T14:01:40.53+00:00

Do you mean to deactivate MFA from office365 or enable it?

Andy David - MVP 142.2K Reputation points MVP

2021-10-12T14:08:53.773+00:00

Deactivate it for that account and allow it to use Basic Auth for SMTP

tuyen1644 21 Reputation points

2021-10-12T14:58:55.01+00:00

I use the account used to send emails that don't have MFA set up, so it's not because of MFA!
Sign in to comment
AgaveJoe 26,136 Reputation points

2021-10-12T16:55:58.7+00:00

According to the MS 365 docs, deprecation of TLS 1.0 and 1.1 started in 2020. Also, according to the docs you can sent unencrypted SMTP which is not recommended though. The best approach is upgrading your systems/software to TLS 1.2.

Preparing for TLS 1.2 in Office 365 and Office 365 GCC
Please sign in to rate this answer.
Vaishnav P 111 Reputation points

2021-10-13T05:05:44.61+00:00

@AgaveJoe Yes, The Application's supports only TLS 1.0 and that has to be upgraded to TLS 1.2.
Sign in to comment
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?
Please sign in to rate this answer.

0 comments No comments
Sign in to comment
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.
Please sign in to rate this answer.

0 comments No comments
Sign in to comment
Maxime Gagnon 6 Reputation points

2021-10-14T21:32:58.633+00:00

Same error here as well with an app developed for thousands of customers. We receive an unusual number of calls of very angry customers regarding this issue which is intermittent.

Of course I can't ask my customers to simply use another email of different providers as they use the same address for numerous years now or use paid office365 accounts...

I also made sure we use compatible version of TLS, and even with 1.1 or 1.2 , it doesn't always work.

Clearly something's wrong with Microsoft SMTP servers...
Please sign in to rate this answer.

1 person found this answer helpful.
Jeremy Motta 1 Reputation point

2021-10-22T19:09:12.683+00:00

Any luck so far? I'm dealing with this same issue. Our ERP software was built on TLS 1.0 and 1.1 and now the system is only sending emails out intermittently. It's bringing our business to a halt.

Maxime Gagnon 6 Reputation points

2021-10-27T19:56:07.88+00:00

No luck.
It seems Microsoft is indeed migrating all their SMTP servers to TLS 1.2 only. So Most attempts with TLS 1.0 or TLS 1.1 will simply not work from what I understand.

It seems the Framework used and the code has both to be updated to take TLS 1.2 into consideration as well.
Sign in to comment