Develop Reference

Why does SmtpClient fail with several different Exceptions when using SSL?

I'm trying to send a mail message using System.Net.Mail.SmtpClient with SSL enabled. While changing no external factors (i.e. hit F5, then hit F5 Again - or even in a loop) it works some times, but most of the times it fails.
Example code:
public void SendMail()
{
using (var client = new SmtpClient())
{
MailMessage mailMessage = new MailMessage();
client.EnableSsl = true;
client.Host = "smtp.example.com";
client.Timeout = 10000;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
mailMessage.From = new MailAddress("from#example.com");
mailMessage.To.Add(new MailAddress("to#example.com"));
mailMessage.Subject = "Test";
mailMessage.Body = "Message " + DateTime.Now.ToString();
try
{
client.Send(mailMessage);
}
catch (Exception ex)
{
// This being a Pokemon block is besides the point
}
}
}
In my catch block I just get a timeout, but if I set up a trace for System.Net and System.Net.Sockets I can see a number of different exceptions:
Unable to read data from the transport connection: A blocking operation was interrupted by a call to WSACancelBlockingCall
Unable to read data from the transport connection: An established connection was aborted by the software in your host machine
Cannot access a disposed object
Reading is not supported on this stream
Writing is not supported on this stream
All of which happen post EHLO, STARTTLS and authentication. The client and the server are chatting along in their cryptographic ways when the exceptions are thrown.
System.Net.Mail.SmtpClient.Send() is the the only frame all call stacks have in common.
Of course I've tried changing the code in a number of ways, such as setting client.UseDefaultCredentials, using client.SendAsync() and whatnot. But I suspect it's something entirely different knocking the connection over at different times - a configuration error on one of the machines involved perhaps?
So I've checked the Event Logs for signs of something messing with the connection, but I haven't found anything.
Any suggestions as to what I should be looking for here?

Sometimes a timeout is just a timeout ...
Digging further into this issue I used Wireshark to see what was going on at the network level.
When the failures happened, the client machine invariably sent a TCP [RST, ACK] packet around 10 seconds after EHLO. A timespan conspicuously close to my timeout value. When I doubled the timeout value the mails came through without failure every single time.
Of course if we were to spend more than 10 seconds sending each mail, we'd soon be queuing up mails for hours in our production system, so I needed to find out why it took so long.
One detail caught my attention:
The client was spending upwards of four seconds between two packets. And it was generally spending hundreds of milliseconds between packets whereas the server would respond within tens.
The next step was to build the code without debug symbols and measure again without a debugger attached. The time spent per e-mail sent immediately went sub-second. Now it's no news to me that code runs slower with a debugger attached, but seeing it run that much slower was a surprise.
So the lessons for me to learn were: Try not to overanalyze, and when timing is involved kill the debugger once in a while.

This should be a comment (I don't have reputation to make comments), but it could be a firewall issue, given you're getting an "Unable to read data from the transport connection: An established connection was aborted by the software in your host machine" error (basically, firewall or anti-virus cancelled your attempt to send a mail).
The error "Unable to read data from the transport connection: A blocking operation was interrupted by a call to WSACancelBlockingCall" happens when a stream is closed - see this question - and the other errors you've listed seem like they're related to trying to access a stream when it's closed, too.
All these error point to a common cause, a connection cancelled somewhere between you and the server and most likely on your machine/ network, and you get different errors depending at what point the effect propagates through to your application.
Another thing is, if you use
Credentials = new NetworkCredential(fromAddress.Address, fromPassword)
then you have to enable ssl afterwards, not before, otherwise it's cleared.

I suppose you have missed to set Credentials property of your host. However the another reason for exceptions may be wrong host name and port.Try something like :
public void SendMail()
{
try
{
var fromAddress = new MailAddress("from#example.com", "Some text");
var toAddress = new MailAddress("to#example.com");
const string fromPassword = "from account password";
var smtp = new SmtpClient
{
Host = "smtp.example.com",
Port = "your host port", //for gmail is 587
EnableSsl = true,
DeliveryMethod = SmtpDeliveryMethod.Network,
UseDefaultCredentials = false,
Credentials = new NetworkCredential(fromAddress.Address, fromPassword)
};
using (var message = new MailMessage(fromAddress, toAddress)
{
Subject = "Test",
Body = "Message " + DateTime.Now.ToString()
})
{
smtp.Send(message);
}
}
catch (Exception ex)
{
//do something
}
}
It is tested with gmail host which is smtp.gmail.com and it works correctly

RabbitMQ throws Shared Queue closed error

We have been using RabbitMQ as messaging service in the project. We will be pushing message into a queue and which will be received at the message consumer and will be trying to make entry into database. Once the values entered into the database we will be sending positive acknowledgement back to the RabbitMQ server if not we will be sending negative acknowledgement.
I have created Message Consumer as Windows service.Message has been successfully entered and well received by the message consumer(Made entry in table)but with an exception log "Shared Queue closed".
Please find the code block.
while (true)
{
try
{
if (!Connection.IsOpen || !Channel.IsOpen)
{
CreateConnection(existConnectionConfig, QueueName);
consumer = new QueueingBasicConsumer(Channel);
consumerTag=Channel.BasicConsume(QueueName,false,consumer);
}
BasicDeliverEventArgs e = (BasicDeliverEventArgs)consumer.Queue.Dequeue();
IBasicProperties props = e.BasicProperties;
byte[] body = e.Body;
bool ack = onMessageReceived(body);
if (ack == true)
{
Channel.BasicAck(e.DeliveryTag, false);
}
else
Channel.BasicNack(e.DeliveryTag, false, true);
}
catch (Exception ex)
{
//Logged the exception in text file where i could see the
//message as "Shared queue closed"
}
}
I have surfed in net too but couldn't able to what the problem. It will be helpful if anyone able to help me out.
Thanks in advance,
Selva

In answer to your question, I have experienced the same problems when my Web Client has reset the connection due to App Pool recycling or some other underlying reason the connection has been dropped that appears beyond your scope. You may need to build in a retry mechanism to cope with this.
You might want to look at MassTransit. I have used this with RabbitMQ and it makes things a lot easier by effectively providing a management layer to RabbitMQ. MassTransit takes away the headache of retry mechanisms - see Connection management. It also provides a nice multi threaded concurrent consumer configuration.
This has the bonus of your implementation being more portable - you could easily change things to MSMQ should the requirement come along.

SmtpClient.Send randomly causes SmtpException 4.7.0 timeout waiting for client input

I can't seem to find the cause for this problem.
Sometimes I get SmtpException "4.7.0 timeout waiting for client input" being thrown on using the following c# code for .net-4.0:
using System;
using System.Net.Mail;
namespace SendMail
{
class Program
{
static void Main(string[] args)
{
for (int i = 0; i < 100; i++)
{
string html = "<h1>TEST</h1>";
using (MailMessage mail = new MailMessage("sender#domain.com", "receiver#domain.com"))
{
mail.Subject = "Test";
mail.IsBodyHtml = true;
mail.Body = html;
using (SmtpClient client = new SmtpClient("<internal ip address>"))
{
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("<user name>", "<password>");
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.Send(mail);
}
}
}
}
}
}
It usually crashes at the second attempt (i == 1).
I am aware I should create a single SmtpClient instance and reuse it in the loop but for the purpose of demonstration and in order to be as close as possible to the real code it has to be this way. While the above isn't quite like my production code it does suffer from the same random problem. I figured that if I could solve the problem with this code then I'd know what to do with my actual code, given that it really is a coding issue to begin with. I'm suspecting an obscure server configuration issue but I'm out of ideas on what it could possibly be.
Odd thing: despite being a timeout issue, the exception is thrown very quickly; there's no delay that would suggest an actual timing out problem.
The mail server is MS exchange-server-2007 running on windows-server-2008 SP2. There's no additional SMTP settings specified in app.config file.
I tried to put the code in a Do...While loop that tries five times to send the email back after putting the thread to sleep for one second. Unfortunately that doesn't help: when it fails, it will also fail at the very next attempts.
I also tried using Thread.Sleep(<delay>) before every calls to client.Send(message) but it made no appearant difference.
Our network admin is adamant on the network running without any issues (no packet drops caused by bad MTU setting or anything like that). He backs this up with the fact that there's only my code that seems to have problems (and he's right) and that it does not only happen on a segment of the network (also right).
It's unlikely that the firewall would be causing this either, as every mail my app sends is using internal addresses.
Anybody has a clue here? It would be much appreciated.
UPDATE:
I seem to be able to reproduce the problem every time when using default credentials instead:
using (SmtpClient client = new SmtpClient("<internal ip address>"))
{
client.UseDefaultCredentials = true;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.Send(mail);
}
UPDATE 2:
Nope. Not every time. Everything now works again (until next time).
I really can't put my finger on it.
UPDATE 3:
Interesting new development today: I attempted to create a new account inside MS Outlook with the same address I use with Exchange. Only this time instead of adding it as an MS Exchange address I tried setting it up as a POP3/SMTP account. Here is what happened upon testing the connection:
It's in french but look at the last line: it is the exact same error message I got with my code. This is a clear indication to me that the issue is not within my code.
Of course, this also means that this whole thread shouldn't be on SO. Still, I hope this extra test can help fellow developers out there who are struggling with a similar issue.

This definitely sounds like a server or network issue. Reference this serverfault post for instance: https://serverfault.com/questions/344684/exchange-2007-email-error-451-4-7-0-timeout-waiting-for-client-input
It could be a firewall problem if there is a firewall between your machine and the exchange server. A firewall blocks ports between ip addresses, it doesn't matter where the email is going at all. Firewalls are the bane of my programming existence, so definitely ask your net admin if there is a firewall between the servers and have him check if it is working.
It could also be something like a bad NIC (network card) on the server or even a bad cable. Yes, your network admin said the network is rock solid... but never trust network admins. ;)
It could also be a problem with YOUR network card, network settings or ethernet cable, actually.
Have you tried running this from different computers?

You can fire if off async like by changing your code as follows. You will need to check the AggregateException to see if something bad happened on any of the executing threads.
static void Main(string[] args)
{
for (int i = 0; i < 100; i++)
{
string html = "<h1>TEST</h1>";
Task.Factory.StartNew(() =>
{
using (MailMessage mail = new MailMessage("sender#domain.com", "receiver#domain.com"))
{
mail.Subject = "Test";
mail.IsBodyHtml = true;
mail.Body = html;
using (SmtpClient client = new SmtpClient("<internal ip address>"))
{
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("<user name>", "<password>");
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.Send(mail);
}
}
}).ContinueWith(aex => {
if (aex.Exception != null)
{
//add some logic to deal with the exception
}
});
}
}

it is better to define SmtpClient before the loop, same problem happened with me and this solved it.
using System;
using System.Net.Mail;
namespace SendMail
{
class Program
{
SmtpClient client = new SmtpClient("<internal ip address>");
static void Main(string[] args)
{
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("<user name>", "<password>");
//client.EnableSsl = true;
//client.Port = 25;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
for (int i = 0; i < 100; i++)
{
string html = "<h1>TEST</h1>";
using (MailMessage mail = new MailMessage("sender#domain.com", "receiver#domain.com"))
{
mail.Subject = "Test";
mail.IsBodyHtml = true;
mail.Body = html;
client.Send(mail);
}
}
}
}
}

I'm fairly new to this messaging issue. I have currently been working on a messaging application and occasionally this exception is thrown into the system.
So far the answers I have picked up on the internet point out that this is an error in the email sender's authentication. Perhaps the limitation of daily submissions and the hourly send limit may inhibit SMTP server authentication of the email. Example, in case smtps.bol.com.br has a limit of 50 emails per hour, having to have a 60 minute interval to send a new batch of messages.
I have done my tests here and I do not have a conclusive answer, but I believe that maybe the way is this. If they find the definitive solution, do not forget to post.

Make sure the objects call .Dispose() in all cases.
I saw this problem on a highly active production system that sends 5000+ emails a day, but the problem would only happen to about 5% of the emails. The code sending the email was written before .Net 4.0, which introduced the Dispose() call to SmtpClient and MailMessage. I made a very simple change to make sure both objects were disposed and have not seen the problem again in 5 days.
That same code that does NOT call Dispose() runs on less active systems without any problems. My theory is there is some kind of cumulative resource leak if you fail to call Dispose() and it only causes this error under heavy load.

I was getting similar error couple of years back on Amazon Aws server. It seems my security company "AllCovered.com" had to do a exception to my server ip address to allow send smtp emails.
I do get this error if anytime a new server created is forgotten to be put in exception.

Sending SMS for a bulk of users

I want to send SMS to bulk of users(4000 user) so i put the following method on loop :
protected int SendSMS(string url)
{
// Now to Send Data.
StreamWriter writer = null;
StringBuilder postData = new StringBuilder();
Uri myUri = new Uri(url);
postData.Append(HttpUtility.ParseQueryString(myUri.Query).Get("Username"));
postData.Append(HttpUtility.ParseQueryString(myUri.Query).Get("Password"));
postData.Append(HttpUtility.ParseQueryString(myUri.Query).Get("Sender"));
postData.Append(HttpUtility.ParseQueryString(myUri.Query).Get("Recipients"));
postData.Append(HttpUtility.ParseQueryString(myUri.Query).Get("MessageData"));
string webpageContent = string.Empty;
byte[] byteArray = Encoding.UTF8.GetBytes(postData.ToString());
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
webRequest.ContentLength = webRequest.ContentLength = byteArray.Length;
writer = new StreamWriter(webRequest.GetRequestStream());
try
{
using (Stream webpageStream = webRequest.GetRequestStream())
{
webpageStream.Write(byteArray, 0, byteArray.Length);
}
using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse())
{
using (StreamReader reader = new StreamReader(webResponse.GetResponseStream()))
{
webpageContent = reader.ReadToEnd();
//TODO:parse webpagecontent: iF response contains "OK"
if (webpageContent.Contains("OK")) return 1;
else return 0;
}
}
//return 1;
}
catch (Exception ee)
{
ErrMapping.WriteLog(url);
string error = ee.Message + "<br><br>Stack Trace : " + ee.StackTrace;
ErrMapping.WriteLog(error);
return -1;
}
}
After a specific number of users like 65 user, no sms had been sent for the rest of users and
I get the following exception :
Error Message:Thread was being aborted.<br><br>Stack Trace : at System.Net.UnsafeNclNativeMethods.OSSOCK.recv(IntPtr socketHandle, Byte* pinnedBuffer, Int32 len, SocketFlags socketFlags)
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, SocketError& errorCode)
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.PooledStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.Connection.SyncRead(HttpWebRequest request, Boolean userRetrievedStream, Boolean probeRead)
at System.Net.ConnectStream.ProcessWriteCallDone(ConnectionReturnResult returnResult)
at System.Net.HttpWebRequest.CheckDeferredCallDone(ConnectStream stream)
at System.Net.HttpWebRequest.GetResponse()
at SendSMS_EmailUI.Frm_SMS_send.SendSMS(String url)

IMHO, the bulk operations that will be performed on behalf of the application can be done easily by the following procedure
When a bulk SMS is triggered, the details will be entered in a database table
A windows service will be constantly monitoring this table for any updates
When the windows service finds the new entries, it will take few records like few hundreds and then send them. Batch Processing.
There can be a delay between consequent requests.
This will ensure you to track which line items have failed and also does not clog the server with the bulk data.
This is a most widely suggested approach.
Please provide your comments on this implementation.

I have built an SMS portal. What you describe was also experienced in v1.0 of my application. The solution was to have my SMS gateway provide me with Bulk SMS access via HTTP. I could put up to 1000 destinations into an XML (or comma delimited) package and send to the Bulk SMS Gateway. Because I run on a shared host, I limited this to 500 destinations.
I have a cache/temporary storage/table where I batch large destination (up to 1,000,000) in some cases and a scheduler (timer based) sends each batch of 500 every few seconds (by calling a script repeatedly) until the messages are sent. Works like charm!
For personalized messages, I encourage the client to use my desktop application for personalization before forwarding to my SMS portal. Good luck
PROCESS:
You'll need three items
The Script that receives the SendSMS request
The script that sends the SMS
The Scheduler/Timer (Script/Host Service)
A. The Send SMS request arrives with
a. The Message and Sender ID/ Sender GSM Number.
b. The Destinations (as a comma delimited list). We'll assume 10,000 destinations
B. Split the destinations into 500 (any size you wish) and log the 500 destinations along with the message and SenderID in each INBOX row/record.
Note: if you count 500 out by looping (10,000 loops), the script could Time out. GSM Numbers in My country are 13 digits.
So I do a loop Sub String of length 500(13+1) to get 500 destinations per batch (20 loops).*
C. Call the Script that Sends the SMS. Sends the first 500 and tag the message as Sent. You can add Time Sent. Start the Scheduler
D. The Scheduler checks every 1.5 minutes if any unsent messages exist in the INBOX and sends it. If nothing, Scheduler Stops.
So, 10,000 messages are sent within 30 mintues

We do something similar to what saravan suggested for email messages, and suspect it will work SMS.
Basically the service that runs on our web server only sends x at a time, and there is a custom delay y between each send.
It can send two thousand in less than ten minutes with neither a CPU nor a bandwidth spike.
Some tips that weren't in our original design to keep in mind:
Have a way to manually stop all sending (see next tip)
Have a user friendly way to terminate a particular message. If your code (or the user) accidentally sends the same thing five times, you want a way to abort it, quickly.
Use a config file for both numbers (x & y above) so you can adjust without redeploying. I think the y delay is 50 ms.
Before you decide to bundle the same message to multiple recipients, make sure that smartphones can't reply to everyone else in their bundle.
HTH,
-Chris C.

I suspect the problem is that because you are on an asp.net website and this is a long-running task that it is timing out the response.
this timeout is controlled in the web.config and it's default is set to 110 seconds. Increase this to a much longer number and see if it starts working.
<system.web>
<!-- 600 seconds = 10 minute timeout --->
<httpRuntime executionTimeout="600"/>
</system.web>
A better approach would be to using a separate thread and returning updates of the progress
to the user, although this would be more complex, but ultimately more reliable.
See Parallel.ForEach for a simple way to thread this process.
Msdn - httpRuntime documention

This is not answering your original question, but is related useful info. Once you solve this problem, you may hit another -- telcos routinely block bulk-sent SMS messages as a way to suppress SMS spam. If you will be doing this on a commercial scale, you will need to file a brief with the Mobile Marketing Association, and get their approval, which can take a considerable amount of time.

check if your StreamWriter is getting disposed
using (StreamWriter writer = new StreamWriter(webRequest.GetRequestStream()))
{
}

May be the buffer value is full please check it and put it to maximum value in web-config file

Maybe your are making web request too fast: try slowing them down to rule out timing problems, for example adding a sleep:
System.Threading.Thread.Sleep(1000);
1000ms = 1 sec is only a hint, you should try different values to see if something changes

SmtpException - The operation has timed out

Here is my code:
SmtpClient client = new SmtpClient();
client.UseDefaultCredentials = true;
using (client as IDisposable)
{
foreach (MailAddress addr in Addresses)
{
if (addr != null)
{
try
{
message.To.Clear();
message.To.Add(addr);
client.Send(message);
}
catch (Exception ex)
{
Log(ex);
}
i++;
}
}
}
every 100 seconds, I log a message saying
The operation has timed out.
Is this a client side setting or on the actual mail server?

The problem happens when you are not able to connect to SMTP server and thats why this timeout message occur. So this message occurs on your client when your client is not able to connect to your SMTP Server:
100 second is default value as described below:
http://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient.timeout.aspx
There could be several issue why this prblem could occur i.e. Wrong SMTP address, SMTP reject, Port setting, SSL configuration etc which you need to fix.

I was also expeiencing this timeout. The problem seemed to be that the email I was trying to send out had a single email address but repeated 30+ times (this was a dev environment where the real recipient email addresses were change to a dev one). Cutting this number (to about 20) resolved the issue. Obviously, this is an issue specific to my own SMTP server, but the recipient list is something to look at if all else fails.