only the first email is being sent in a For Loop of a Window Service

Question

I want to send an email to more than 2 people using my own database. So I use for loop to send an email. But it is just sent it to a first person. I also check that the email_data has more than 2, and I bring the email data well. Here is my code.

    private void Email()
    {
        DataTable email_data = GetEmailData();
           .....
                String from = "aa@gmail.com";

                for (int i = 0; i <= email_data.Rows.Count; i++)
                {
                    String to = email_data.Rows[i][0].ToString();

                    using (MailMessage mm = new MailMessage(from, to))
                    {

                        SmtpClient smtp = new SmtpClient();
                        mm.Subject = "List";
                        mm.Attachments.Add(new Attachment(new MemoryStream(bytes), "List.xlsx"));
                        mm.IsBodyHtml = true;

                        smtp.Host = "smtp.gmail.com";
                        smtp.EnableSsl = true;
                        System.Net.NetworkCredential credentials = new System.Net.NetworkCredential();
                        credentials.UserName = "aa@gmail.com";
                        credentials.Password = "aa";
                        smtp.UseDefaultCredentials = true;
                        smtp.Credentials = credentials;
                        smtp.Port = 587;
   //works well in the first loop, but stops here in the second loop
                        smtp.Send(mm);
                    }
                }
        }

Although it is probably not cause of your problem, please note that `SmtpClient` and `Attachment` implements `IDisposable` so you should enclose them in `using(...)` statement — Ňuf, Jun 05 '17 at 17:09
@Nuf I think I use using(...) statement, you mean for loop also should be enclosed by using() statement? — Scarlett, Jun 05 '17 at 17:18
I mean `using(SmtpClient smtp = new SmtpClient()) {...}` and `using(Attachment(new MemoryStream(bytes), "List.xlsx")) {...}` — Ňuf, Jun 05 '17 at 17:21
@Nuf I try that but still doesn't work.. For the first email, it is sent perfect, but when I go to 2nd for loop , it just stopped before smtp.Send(mm). — Scarlett, Jun 05 '17 at 19:23

score 0 · Answer 1 · answered Jun 05 '17 at 16:51

check the row count by adding debug prints

And also try putting sleep at the end

                    smtp.UseDefaultCredentials = true;
                    smtp.Credentials = credentials;
                    smtp.Port = 587;
                    smtp.Send(mm);

System.Threading.Sleep(1000);

score 0 · Accepted Answer · answered Jun 06 '17 at 09:13

I tried to run your code on my computer (I just replaced credentials with my private gmail account credentials) and it worked without any problem - emails was successfully sent to 3 different email addresses. So problem might be related to your computer. So here are a few ideas what you can try:

run your program on different computer to see if it works there (for comparison, I run it successfully on Windows 10 Home, Visual Studio 2017 CE, Console Application targeting .NET Framework 4.7)
check your antivirus and firewall if they are not somehow blocking mass email sending.
try to debug source code of SmtpClient.Send() method to see where exactly execution stops, which should give you a hint what is wrong and how to fix it.
in app.config enable detailed logging of network communication and see if there isn't some problem when connecting to SMTP server.

BTW there is probably bug: for (int i = 0; i <= email_data.Rows.Count; i++) should be for (int i = 0; i < email_data.Rows.Count; i++)

That's so strange...It still doesn't work I decide to use BCC instead of those. anyway thank you..! — Scarlett, Jun 07 '17 at 16:29

only the first email is being sent in a For Loop of a Window Service

2 Answers2