C# how can I send bulk mail with mailkit?

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Hi everyone I'm coding bulk mail sender application with c# doing part by part and when I send single mail everything is fine I'm not getting any problem bu when I want to send bulk mail for example to 5 recipient I'm getting an error 4 time the error message is "The Smtp Client Not Connected" 1 time "Message Sent" so out of 5 mails only 1 mail sending

C#

using MailKit.Net.Smtp;
using MailKit;
using MimeKit;

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            CheckForIllegalCrossThreadCalls = false;

            BodyBuilder builder = new BodyBuilder();
            builder.HtmlBody = rchtxtboxebody.Text;

            MimeMessage message = new MimeMessage();
            message.Subject = txtsubject.Text;
            message.Body = builder.ToMessageBody();

            SmtpClient sc = new SmtpClient();
            sc.Timeout = 3000;
            sc.AuthenticationMechanisms.Remove("XOAUTH2");

            sc.Connect(txthostname.Text, int.Parse(txtport.Text), chkssl.Checked);
            sc.Authenticate(txtusername.Text, txtpassword.Text);
            foreach (string email in lstleads.Items)
            {
                try
                {
                    message.From.Add(new MailboxAddress(txtfromname.Text, txtfrommail.Text));
                    message.To.Add(MailboxAddress.Parse(email));
                    sc.Send(message);

                    Thread.Sleep(3000);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    sc.Disconnect(true);
                }
            }

        }

this is the my code I'm using where is problem?

What I have tried:

I tried to change timeout to 10000 but not worked

Posted 17-May-22 2:32am

YusufA0

Updated 6-Feb-23 22:51pm

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2 solutions

Solution 2

why don't you use a BCC array instead of loop by email addresses?

Posted 6-Feb-23 22:51pm

Владимир Береза

Comments

Dave Kreskowiak 7-Feb-23 9:24am

I seriously doubt the OP is still working on this a year later.

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Richard Deeming · Accepted Answer · 2022-05-17T02:45:00

The finally { sc.Disconnect(true); } block inside your loop causes the client to disconnect after the first message is sent, and you never try to reconnect it.

You also don't clear the recipient list after the first message. If you send 10 messages, the first recipient will receive 10 copies, each one with one more address from your list appended to it. The second recipient will receive 9 messages, and so on.

C#

try
{
    foreach (string email in lstleads.Items)
    {
        message.To.Clear();
        message.To.Add(MailboxAddress.Parse(email));
        sc.Send(message);
        Thread.Sleep(3000);
    }
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}
finally
{
    sc.Disconnect(true);
}

NB: This sort of code is highly likely to get your email account banned for spamming.