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 24,281 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 24,281 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

Subhi Almohtasib 16 Reputation points

2021-10-15T13:41:29+00:00

Hello All,

I was facing the same issue until I upgraded the .NET version to 4.6 instead of 4.5. Please refer to this answer here
https://stackoverflow.com/a/45442874/9050439

Hopefully it helps you.

Thanks
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3 people found this answer helpful.
tuyen1644 21 Reputation points

2021-10-20T07:55:05.07+00:00

Thank you...! Currently, I'm using .net 4.7.2 and still getting this error

Dan Azari 0 Reputation points

2023-06-15T21:32:12.0366667+00:00

Changing from .NET 4.5 to 4.6 worked for me as well.
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Andy David - MVP 141K Reputation points MVP

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

Is MFA required for this account? If so, that is expected.
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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 141K 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!
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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...
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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.
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Evan Knutson 6 Reputation points

2021-10-14T21:47:06.507+00:00
An update on my end. The issue is resolved. Forcing TLS1.2 was the fix. I upgraded from .NET 2... to .NET v4.0.30319 and set the below:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12; SmtpClient.TargetName = "STARTTLS/" + EmailServer;

I then had issues with registering the new .dll (i spoke incorrectly in my comment above). So when I thought the switch the TLS1.2 was not the fix, that was incorrect, the issue was that the .dll was not updating in the gac. I had to use an updated version of regasm.exe, found an updated version of gacutil.exe and also updated gacutil.exe.config.

so for example I am using this to register:
%windir%\Microsoft.NET\Framework\v4.0.30319\regasm.exe "C:\Program Files (x86)[app directory here]\DNeMailer.dll" /tlb:"C:\Program Files (x86)[app directory here]\DNeMailer.tlb"

And then to install into the gac. I had to update the version of .NET referenced in gacutil.exe.config.
"C:\Program Files (x86)[app directory here]\gacutil.exe" /i "C:\Program Files (x86)[app directory here\DNeMailer.dll"

It became obvious to me that the .dll was not updating when I was not able to uninstall the .dll from C:\Windows\assembly\
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AgaveJoe 26,181 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
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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.
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