System.Net.Mail.SmtpException: Insufficient system storage. The server response was: 4.3.1 Insufficient system resources

Question

I've recently designed a program in C# that will pull information from SQL databases, write an HTML page with the results, and auto-email it out. I've got everything working [sporadically], the problem I'm having is that I seem to be crashing our company's exchange server. After the first few successful runs of the program, I'll start getting this exception:

Base exception: System.Net.Mail.SmtpException: Insufficient system storage. The server response was: 4.3.1 Insufficient system resources

I'm wondering if I should be calling some sort of Dispose()-like method in my mailing? Or if there is any other apparent reason that I would be causing the mail system to stop responding? This affects all clients in our company, not just my code.

This is Exchange 2010, and my code is compiled against .NET 3.5. My attachments are typically 27kb. If I log into the exchange server, it seems that messages just stick in a queue indefinitely. Clearing out the queue (remove without sending NDR) and rebooting the server will get it going again.

The mailing portions look like this (username, password, and address changed):

public void doFinalEmail()
{
     List<string> distList = new List<string>();
     string distListPath = Environment.CurrentDirectory + "\\DistList.txt";
     string aLine;

     logThat("Attempting email distribution of the generated report.");

     if (File.Exists(distListPath))
     {
         FileInfo distFile = new FileInfo(distListPath);
         StreamReader distReader = distFile.OpenText();

         while (!String.IsNullOrEmpty(aLine = distReader.ReadLine()))
         {
             distList.Add(aLine);
         }
     }
     else
     {
         logThat("[[ERROR]]: Distribution List DOES NOT EXIST! Path: " + distListPath);
     }

     MailMessage msg = new MailMessage();
     MailAddress fromAddress = new MailAddress("emailaddresshere");
     msg.From = fromAddress;

     logThat("Recipients: ");
     foreach (string anAddr in distList)
     {
         msg.To.Add(anAddr);
         logThat("\t" + anAddr);
     }
     if (File.Exists(Program.fullExportPath))
     {
         logThat("Attachment: " + Program.fullExportPath);
         Attachment mailAttachment = new Attachment(Program.fullExportPath);
         msg.Attachments.Add(mailAttachment);
         string subj = "Company: " + Program.yestFileName;
         msg.Subject = subj;
         msg.IsBodyHtml = true;
         msg.BodyEncoding = System.Text.Encoding.UTF8;
         sendMail(msg);
     }
     else
     {
         logThat("[[ERROR]]: ATTACHMENT DOES NOT EXIST! Path: " + Program.fullExportPath);
     }
 }

 public void sendMail(MailMessage msg)
 {
     try
     {
         string username = "user"; //domain user
         string password = "pass"; // password
         SmtpClient mClient = new SmtpClient();
         mClient.Host = "192.168.254.11";
         mClient.Credentials = new NetworkCredential(username, password);
         mClient.DeliveryMethod = SmtpDeliveryMethod.Network;
         mClient.Send(msg);
     }
     catch (Exception oops)
     {
         string whatHappened = String.Format("Company: \r\nFailure in {0}! \r\n\r\nError message: {1} \r\nError data: {2} \r\n\r\nStack trace: {3} \r\n\r\nBase exception: {4} \r\nOccuring in method: {5} with a type of {6}\r\n", oops.Source, oops.Message, oops.Data, oops.StackTrace, oops.GetBaseException(), oops.TargetSite, oops.GetType());
         logThat(whatHappened);
         Environment.Exit(1);
     }
 }

Answer 1

This error can happen when:

1. The exchange server is out of disk space.
2. The recipient mailbox is out of disk space.

It is more common to run into issue #2 than issue #1.

Here is a list of Exchange Status Codes and their meanings.