当我运行代码，并发送它显示发送失败

Question

嗨，大家好，我有问题发送群发邮件使用Windows窗体中的列表框......它显示发送失败，当我尝试发送大宗邮件..这里是我的代码我不知道我检查和检查的代码有什么问题

void SendMail1(string from,string to,string subject,string message,string host,int port,string un,string pw) 
    { 
     MailMessage tm = new MailMessage(); 
     tm.From = new MailAddress(from); 
     tm.To.Add(new MailAddress(to)); 
     tm.Subject = subject; 
     tm.Body = message; 
     tm.IsBodyHtml = true; 
     tm.Priority = MailPriority.Normal; 
     tm.SubjectEncoding = Encoding.UTF8; 
     var smtp = new SmtpClient(); 
     { 
      smtp.Host = host; 
      smtp.Port = port; 
      smtp.EnableSsl = true; 
      smtp.UseDefaultCredentials = true; 
      smtp.DeliveryMethod = SmtpDeliveryMethod.Network;    
      //default credentials 
      smtp.Credentials = new NetworkCredential(un,pw); 
     } 
     smtp.Send(tm); 
     MetroFramework.MetroMessageBox.Show(this, "Bulk Mail Successfully Sent.....", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information); 
    } 


    private void btnSendEmail2_Click(object sender, EventArgs e) 
    { 
     try 
     { 
      if (string.IsNullOrEmpty(txtSubject2.Text) || string.IsNullOrEmpty(txtMessage2.Text) || string.IsNullOrEmpty(txtFrom2.Text) || string.IsNullOrEmpty(txtEmailAddress2.Text) || string.IsNullOrEmpty(txtPassword2.Text) || string.IsNullOrEmpty(txtAttachment2.Text)) 
      { 
       MetroFramework.MetroMessageBox.Show(this, "One Or More Fields Empty..Please Check To See Which Fields Are Empty,Before Sending Mails...", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning); 
      } 
      else 
      { 
       //send mails here 
       foreach(string i in lstEmails.Items) 
       { 
        if (i.Trim() != string.Empty) 
        { 
         //declare all fields 
         DataTable dt = new DataTable("tblEmails"); 
         dt.Columns.Add("Email", typeof(string)); 
         dt.Rows.Add(i.ToString()); 
         string _from = txtFrom2.Text.Trim(); 
         string _subject = txtSubject2.Text.Trim(); 
         string _message = txtMessage2.Text.Trim(); 
         string _host = Convert.ToString(ddlProvider2.SelectedItem); 
         int _port = 587; 
         string _un = txtEmailAddress2.Text.Trim(); 
         string _pw = txtPassword2.Text.Trim(); 
         Parallel.ForEach(dt.AsEnumerable(), x => 
         { 
          SendMail1(_from, x["Email"].ToString(), _subject,_message 
           , _host, _port, _un, _pw); 
         }); 

         // MetroFramework.MetroMessageBox.Show(this, i + "\n", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information); 
        } 
        else 
        { 
         MetroFramework.MetroMessageBox.Show(this, "Please Load Some Emails To Send Mail Message...", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning); 
        } 
       } 
      } 
     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK); 
     } 
    } 

Answer 1

您试图发送电子邮件批量。如果“有时”有效，那么如果您的发送速率高于管理员设置的阈值，SMTP服务器很可能会拒绝您的消息。如果情况确实如此，您可以做的事情不多，除非管理员将更改其政策以适应您的应用程序。或者，您需要一个不同的SMTP服务（亚马逊有一个，仅用于像您这样的批量邮件应用程序）。