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Asked: 2026-05-26T17:06:17+00:00

I am sending emails using c# using SmtpClient. I have to send aproximately one

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I am sending emails using c# using SmtpClient. I have to send aproximately one hundred different emails per day, and I can’t use the same mail (adding several recipients) since the email changes according to the recipient.

I am not using a local SMTP server, and I understand (according to @rizzle response here)
that some time has to be left between one mail and another one. However, I am sleeping my program for 10 seconds and still, it is only the first email that gets sent, never the second one (so far I am trying my system with two emails instead of one hundred). This is my code, any ideas?

foreach (Person p in clientList)
            {
                AlternateView plainView = AlternateView.CreateAlternateViewFromString("Texto visible para clientes que no tienen HTML", null, "text/plain");
                //AlternateView htmlView = AlternateView.CreateAlternateViewFromString("Here is an embedded image.<img src=cid:companylogo>", null, "text/html");

                string htmlString = "html string body of the email";
                AlternateView htmlView = AlternateView.CreateAlternateViewFromString(htmlString, null, "text/html");

                System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage();
                message.AlternateViews.Add(htmlView);
                message.To.Add(p.email.Trim());
                message.Subject = p.nombre+", email subject";
                message.From = new System.Net.Mail.MailAddress(fromAddress);
                System.Net.Mail.SmtpClient client = new System.Net.Mail.SmtpClient("...");
                NetworkCredential myCreds = new NetworkCredential(usr, pass, "");
                client.Credentials = myCreds;
                client.Send(message);
                System.Threading.Thread.Sleep(10000);

            }
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1 Answer

  1. Editorial Team

    Do client.Dispose() right after you send your last message, if you’re on dotnet 4. This will force the dotnet SMTP stuff to finish its work.

    See here: System.Net.Mail and MailMessage not Sending Messages Immediately

    If you’re on earlier versions of DotNet, try doing a couple of things.

    Do message.Dispose() when you’re done with the message instance.

    Define your SmtpClient locally (within a method) and exit the method when you’re done sending. That is, don’t try to keep your client instance around as a field in one of your long-lived class instances; it won’t flush the last message you sent to the server until it’s finalized.

    (They really did fix this in dotnet 4.0)

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