"The function requested is not supported" exception when using SmtpClient in Azure role

Question

I'm getting an exception when using SmtpClient in an Azure Web or Worker role.

I created a console app to manually run on the role VMs via RDP to reproduce:

using System;
using System.Net;
using System.Net.Mail;
using System.Text;

namespace ConsoleApplication1
{
   class Program
   {
      static void Main()
      {
         var mailClient = new SmtpClient("mail.redacted.com", 587);
         mailClient.EnableSsl = true;
         mailClient.DeliveryFormat = SmtpDeliveryFormat.International;
         mailClient.DeliveryMethod = SmtpDeliveryMethod.Network;

         mailClient.UseDefaultCredentials = false;//SET THIS FIRST OR IT WIPES OUT CREDENTIALS
         NetworkCredential netCreds = new NetworkCredential("[email protected]", "12345 same combination on my luggage");
         mailClient.Credentials = netCreds;

         MailMessage message = new MailMessage();
         message.SubjectEncoding = Encoding.UTF8;
         message.BodyEncoding = Encoding.UTF8;
         message.IsBodyHtml = false;

         message.From = new MailAddress("[email protected]");
         message.To.Add(new MailAddress("[email protected]"));

         message.Subject = "testing " + DateTime.UtcNow;
         message.Body = "The quick brown fox jumped over the lazy dogs.";

         mailClient.Send(message);
      }
   }
}

Locally it sends an email just fine. On Azure I get this:

    Unhandled Exception: System.Net.Mail.SmtpException: Failure sending mail. ---> System.ComponentModel.Win32Exception: The function requested is not supported
       at System.Net.NTAuthentication.GetOutgoingBlob(Byte[] incomingBlob, Boolean throwOnError, SecurityStatus& statusCode)
       at System.Net.NTAuthentication.GetOutgoingBlob(String incomingBlob)
       at System.Net.Mail.SmtpNtlmAuthenticationModule.Authenticate(String challenge, NetworkCredential credential, Object sessionCookie, String spn, ChannelBinding channelBindingToken)
       at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
       at System.Net.Mail.SmtpClient.Send(MailMessage message)
       --- End of inner exception stack trace ---
       at System.Net.Mail.SmtpClient.Send(MailMessage message)
       at ConsoleApplication1.Program.Main() in c:\development\ConsoleApplication1\ConsoleApplication1\Program.cs:line 39

I've confirmed that the Azure machines can access port 587 on the mail server by running TCPing.exe on the Azure roles via RDP.

Mike Asdf Mike Asdf · Accepted Answer · 2013-06-28T21:27:39

So apparently the problem was a mismatched NTLM version between servers.

After logging into the Azure roles and disabling the setting "Require NTLMv2 security" for clients, then it worked:

enter image description here

(Thanks to this answer and this answer for inspiration.)

Currently seeing if we can get our SMTP server upgraded to be NTLMv2-compatible. Otherwise we'll have to set up some automated code to somehow disable that setting on each generated role instance.

Apparently this code worked last month. So I'm guessing a recent Azure OS upgrade changed the default settings.

FYI: The registry key for this setting is

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0] "NtlmMinClientSec"=dword:20000000

To automate setting the registry key add a startup task containing a reg add command like this:

reg add HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0 ^
 /v NtlmMinClientSec ^
 /t REG_DWORD ^
 /d 0x20000000 ^
 /f

where /f forces the current setting to be overwritten and ^ just allows to break the command into multiple lines for better readability. Also make sure to save the command in ASCII encoding to prevent issues during role startup.

"The function requested is not supported" exception when using SmtpClient in Azure role

1 Answers