“Unable to read data from the transport connection

2020-05-29 13:02发布

Unable to test sending email from .NET code in Windows Vista Business.

I am writing code which I will migrate to an SSIS Package once it its proven. The code is to send an error message via email to a list of recipients.

The code is below, however I am getting an exception when I execute the code.

I created a simple class to do the mailing... the design could be better, I am testing functionality before implementing more robust functionality, methods, etc.

namespace LabDemos
{
    class Program
    {
        static void Main(string[] args)
        {
            Mailer m = new Mailer();
            m.test();    
        }
    }
}

namespace LabDemos
{
    class MyMailer
    {    
        List<string> _to = new List<string>();
        List<string> _cc = new List<string>();
        List<string> _bcc = new List<string>();
        String _msgFrom = "";
        String _msgSubject = "";
        String _msgBody = "";            

        public void test(){
        //create the mail message
        MailMessage mail = new MailMessage();

        //set the addresses
        mail.From = new MailAddress("me@domain.com");            

        //set the content
        mail.Subject = "This is an email";
        mail.Body = "this is a sample body";
        mail.IsBodyHtml = false;    

        //send the message
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "emailservername";
        smtp.Port = 25;
        smtp.UseDefaultCredentials = true;
        smtp.Send(mail);            
    }
}

Exception Message

Inner Exception
{"Unable to read data from the transport connection: net_io_connectionclosed."}

Stack Trace
"   at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)\r\n   at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)\r\n   at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)\r\n   at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)\r\n   at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)\r\n   at System.Net.Mail.SmtpClient.GetConnection()\r\n   at System.Net.Mail.SmtpClient.Send(MailMessage message)"


Outer Exception
  System.Net.Mail.SmtpException was unhandled
  Message="Failure sending mail."
  Source="System"
  StackTrace:
       at System.Net.Mail.SmtpClient.Send(MailMessage message)
       at LabDemos.Mailer.test() in C:\Users\username\Documents\Visual Studio 2008\Projects\LabDemos\LabDemos\Mailer.cs:line 40
       at LabDemos.Program.Main(String[] args) in C:\Users\username\Documents\Visual Studio 2008\Projects\LabDemos\LabDemos\Program.cs:line 48
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
       at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel)
       at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly()
       at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData)
       at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext)
       at System.Activator.CreateInstance(ActivationContext activationContext)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: System.IO.IOException
       Message="Unable to read data from the transport connection: net_io_connectionclosed."
       Source="System"
       StackTrace:
            at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)
            at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)
            at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)
            at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
            at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
            at System.Net.Mail.SmtpClient.GetConnection()
            at System.Net.Mail.SmtpClient.Send(MailMessage message)
       InnerException: 

11条回答
做个烂人
2楼-- · 2020-05-29 13:38

Restart IIS. I know this sounds silly, to do a restart for everything. (and sorry to bump up an old thread). But sometimes restarting IIS works magic. I faced the exact same issue and restarting solved it.

Might have happened cause temporarily the name 'localhost' couldn't be resolved. I;m just posting here so that someone who faces it now will probably try this quick fix before attempting to investigate further. Hope it helps

We Are One
3楼-- · 2020-05-29 13:40

If you've specified an IP address in the SMTP Service settings then make sure you're specifying that IP address of the machine within IIS7 and not putting localhost.

IIS7 makes it easy to select 'localhost' but that will lead to this error if the IP for instance is 10.0.0.1

戒情不戒烟
4楼-- · 2020-05-29 13:40

I am facing this issue last 6hr and I am new on that so I am trying to solve this issue in following way

1) I opened command prompt (e.g. Ctrl + R type cmd and enter).
2) And check to SMTP server ping and check response.
3) If it’s gets response then it’s ok and to move next step 4 other wise smtp name is wrong.
4) Then I check by telnet smtp port (e.g. 25 ) is open or not.
5) Using this cmd we check the SMTP response.
6) telnet "yoursmtpname" "portno” (e.g. telnet smtp.gmail.com 25)
7) If telnet is not working, please install or add from control panel in add new features.
8) If it’s working then it’s pass result like.
9) 220 mx.google.com ESMTP .

Using above steps we can find out smtp connection is ready or not to sending mail.

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Rolldiameter
5楼-- · 2020-05-29 13:43

There are several things that can cause this problem, and here are some of the things that I've found. Questions: You mention "Exchange" -- Is this an exchange server? Does the host require authentication (maybe you need to add authentication to the client)? What I would try doing first is assigning the host to the static IP address instead of the host name to see if that works first. If it does then it's most likely a problem with the DNS mapping.

If you are running your exchange server with Virtualization, you need to configure the SmtpClient to the host IP of the Virtual Server, not the physical hosting server name or IP. Right click on Default SMTP virtual server, select Properties, then go to Access tab, click Relay then add the IP address of the computer that send SMTP request to the SMTP server. (ASP.net site)

If this doesn't work, it's because the server is blocking you from sending SMTP packets. You need to make sure to add the box you are sending the SMTP messages from to the SMTP server. This is done through IIS's authentication tab.

I would also like to point out that you should dispose the mail client, or use the client in a "using" statement. This will make sure that the "QUIT" is sent to the server and gracefully close the connection.

using(SmtpClient smtp = new SmtpClient())
{
    smtp.Host = "emailservername";
    smtp.Port = 25;
    smtp.UseDefaultCredentials = true;
    smtp.Send(mail)
}
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一纸荒年 Trace。
6楼-- · 2020-05-29 13:44

If you are using localhost (Use Localhost) in IIS 7, then change it to IP address of the machine instead of localhost or 127.0.0.1

Also follow below link to update your mail server relay accordingly:

Mailbox unavailable. The server response was: 5.7.1 Unable to relay for abc@xyz.com

爷、活的狠高调
7楼-- · 2020-05-29 13:46

Is your code incompleted.Dash is correct in identifying it.Other then that check smtp component is installed or not check link text

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