Q: send bulk Email( more than 100 mails) I am using smtp.corp to send emails from ASP.NET site.
When selecting 50 mails, here all the  mails are sent (it shows the status as sent), but only few members are receiving mails (just 10 members). How to send bulk email in asp.net??
If am selecting 15 mails, 10 mails are sending, but the remaining are not sending. I am getting this error from SMTP server for remaining emails:

Service not available, closing transmission channel. The server
  response was: Too many concurrent SM

System.Net.Mail.MailMessage MyMailMessage = new System.Net.Mail.MailMessage();
try
{
    if (From == "") From = GetConfigVal("emailfrom");

    //System.Net.Mail.MailMessage MyMailMessage = new 
    System.Net.Mail.MailMessage(From, To, Subject, MailBody);
    if (FromName.Trim() != "")
    {
        MyMailMessage.From = new System.Net.Mail.MailAddress(From, FromName);
    }
    else
    {
        MyMailMessage.From = new System.Net.Mail.MailAddress(From);
    }

    MyMailMessage.To.Add(To);
    MyMailMessage.Subject = Subject;
    MyMailMessage.Body = MailBody;

    if (ReplyEmailID.Trim() != "")
    {
        MyMailMessage.ReplyToList.Add(new  
        System.Net.Mail.MailAddress(ReplyEmailID));
    }

    if (CC.Trim() != "")
    {
        MailAddress copy = new MailAddress(CC);
        MyMailMessage.CC.Add(copy);
    }

    MyMailMessage.IsBodyHtml = isHTML;

    //Proper Authentication Details need to be
    // passed when sending from gmail

    System.Net.NetworkCredential mailAuthentication = new
    System.Net.NetworkCredential(GetConfigVal("smtpuser"), 
    GetConfigVal("smtppassword"));

    //For different server like yahoo this details changes and you can
    //get it from respective server.
    System.Net.Mail.SmtpClient mailClient = new System.Net.Mail.SmtpClient(GetConfigVal("smtp"),                              int.Parse(GetConfigVal("smtpport")));
    //Enable SSL
    //mailClient.EnableSsl = true;

    //mailClient.Port = 25;
    mailClient.EnableSsl = false;

    //mailClient.UseDefaultCredentials = true;

    mailClient.Credentials = mailAuthentication;
    mailClient.Send(MyMailMessage);

}


A: It sounds like the server has told you your problem -- too many concurrent connections.
It's difficult to effectively mass email from your own servers, as many servers have safeguards to prevent people from sending bulk email (for good reason)... either programatically or even from your own inbox.
You'll likely either need to 


*

*Write a service that staggers email sends

*If it is the same message, send one message and BCC everyone

*Use a legitimate bulk mail program
I think 2 or 3 are your only real options. Even if you do bypass the SMTP error, like @Alexandre said, they'd probably just end up in the SPAM box of the user... And if you start sending bulk mail from your server, you are going to have to start worrying about things like "sender reputation", lest your IP ends up blacklisted as a "spammer" and major email providers simply decide to not send your email at all. This can ruin your ability to even send a single "Thanks for registering" email when a person registers.
Granted, 100 emails really isn't that much, so 1 may be an option. But considering your code notes reference Gmail, then you will run into more problems in the future, as they actively prohibit sending bulk mail from their servers. 
