How to fix (the operation has timed out) error in sending emails using SMTP?
<p>I need to develop a mailing system in the intranet web-based application that I am working on it for my company. I am developing it with ASP.NET and C#. The purpose of this system is to let the admin to be able to send emails to the users. I developed this system and I tested for 25 users and it works fine. </p>

<p>Now, I have 386 users in the database, so when I tried to send them emails, I got the following error: </p>

<blockquote>
  <p>Exception Details: System.Net.Mail.SmtpException: The operation has
  timed out. 
  I think this is because of ISP in my company blocked sending email to many users after a certain number of milliseconds. I tried to use SendAsync but I found it will not benefit me. </p>
</blockquote>

<p>Also, I tried to maximize the execution timeout in the Web.config file as folloiwng:</p>

<pre><code>&lt;location path="Email4.aspx"&gt;
        &lt;system.web&gt;
                &lt;httpRuntime executionTimeout="180"/&gt;
        &lt;/system.web&gt;
&lt;/location&gt;
</code></pre>

<p>but I failed. <strong>So how to fix this problem?</strong></p>

<p>My Code-Behind (C#):</p>

<pre><code>protected void Page_Load(object sender, EventArgs e)
    {
        SendEmailTOAllUser();
    }


    protected void SendEmail(string toAddresses, string fromAddress, string MailSubject, string MessageBody, bool isBodyHtml)
    {
        SmtpClient sc = new SmtpClient("MAIL.companyDomainName.com");
        try
        {
            MailMessage msg = new MailMessage();
            msg.From = new MailAddress("pssp@companyDomainName.com", "PMOD Safety Services Portal (PSSP)");

            // In case the mail system doesn't like no to recipients. This could be removed
            //msg.To.Add("pssp@companyDomainName.com");

            msg.Bcc.Add(toAddresses);
            msg.Subject = MailSubject;
            msg.Body = MessageBody;
            msg.IsBodyHtml = isBodyHtml;
            //Response.Write(msg);
            sc.Send(msg);
        }
        catch (Exception ex)
        {
            throw ex;
        }

    }

    protected void SendEmailTOAllUser()

    {
        string connString = "Data Source=localhost\\sqlexpress;Initial Catalog=psspEmail;Integrated Security=True";

        using (SqlConnection conn = new SqlConnection(connString))
        {
            var sbEmailAddresses = new System.Text.StringBuilder(1000);
            string quizid = "";

            // Open DB connection.
            conn.Open();

            string cmdText = "SELECT MIN (QuizID) As mQuizID FROM dbo.QUIZ WHERE IsSent &lt;&gt; 1";
            using (SqlCommand cmd = new SqlCommand(cmdText, conn))
            {
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                {
                    while (reader.Read())
                    {
                        // There is only 1 column, so just retrieve it using the ordinal position
                        quizid = reader["mQuizID"].ToString();

                    }
                }
                reader.Close();
            }

            string cmdText2 = "SELECT Username FROM dbo.employee";
            using (SqlCommand cmd = new SqlCommand(cmdText2, conn))
            {
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader != null)
                {
                    while (reader.Read())
                    {
                        var sName = reader.GetString(0);
                        if (!string.IsNullOrEmpty(sName))
                        {
                            if (sbEmailAddresses.Length != 0)
                            {
                                sbEmailAddresses.Append(",");
                            }
                            // Just use the ordinal position for the user name since there is only 1 column
                            sbEmailAddresses.Append(sName).Append("@companyDomainName.com");
                        }
                    }
                }
                reader.Close();
            }

            string cmdText3 = "UPDATE dbo.Quiz SET IsSent = 1 WHERE QuizId = @QuizID";
            using (SqlCommand cmd = new SqlCommand(cmdText3, conn))
            {
                // Add the parameter to the command
                var oParameter = cmd.Parameters.Add("@QuizID", SqlDbType.Int);
                // Get a local copy of the email addresses
                var sEMailAddresses = sbEmailAddresses.ToString();


                    string link = "&lt;a href='http://pmv/pssp/StartQuiz.aspx?testid=" + quizid + "'&gt; Click here to participate &lt;/a&gt;";
                    string body = @"Good day, &lt;br /&gt;&lt;br /&gt;
                                &lt;b&gt; Please participate in the new short safety quiz &lt;/b&gt;"
                                        + link +
                                        @"&lt;br /&gt;&lt;br /&gt;
                            Also, give yourself a chance to gain more safety culture by reading the PMOD Newsletter.
                            &lt;br /&gt; &lt;br /&gt;&lt;br /&gt; &lt;br /&gt;
                            This email was generated using the &lt;a href='http://pmv/pssp/Default.aspx'&gt;PMOD Safety Services Portal (PSSP) &lt;/a&gt;. 
                            Please do not reply to this email.
                            ";

                    SendEmail(sEMailAddresses, "", "Notification of New Weekly Safety Quiz", body, true);

                    // Update the parameter for the current quiz
                    oParameter.Value = quizid;
                    // And execute the command
                    cmd.ExecuteNonQuery();
            }
            conn.Close();
        }
    }
</code></pre>
