System.Net.Mail and MailMessage not Sending Messages Immediately

Question

When I sent a mail using System.Net.Mail, it seems that the messages do not send immediately. They take a minute or two before reaching my inbox. Once I quit the application, all of the messages are received within seconds though. Is there some sort of mail message buffer setting that can force SmtpClient to send messages immediately?

public static void SendMessage(string smtpServer, string mailFrom, string mailFromDisplayName, string[] mailTo, string[] mailCc, string subject, string body)
{
    try
    {
        string to = mailTo != null ? string.Join(",", mailTo) : null;
        string cc = mailCc != null ? string.Join(",", mailCc) : null;

        MailMessage mail = new MailMessage();
        SmtpClient client = new SmtpClient(smtpServer);

        mail.From = new MailAddress(mailFrom, mailFromDisplayName);
        mail.To.Add(to);

        if (cc != null)
        {
            mail.CC.Add(cc);
        }

        mail.Subject = subject;
        mail.Body = body.Replace(Environment.NewLine, "<BR>");
        mail.IsBodyHtml = true;

        client.Send(mail);
    }
    catch (Exception ex)
    {
        logger.Error("Failure sending email.", ex);
    }

Thanks,

Mark

Answer 1

Try this, if you're on Dotnet 4.0

using (SmtpClient client = new SmtpClient(smtpServer))  
{
    MailMessage mail = new MailMessage();
    // your code here.

    client.Send(mail);
}

This will Dispose your client instance, causing it to wrap up its SMTP session with a QUIT protocol element.

If you're stuck on an earlier dotnet version, try arranging to re-use the same SmtpClient instance for each message your program sends.

Of course, keep in mind that e-mail is inherently a store-and-forward system, and there is nothing synchronous (or even formally predictable) about delays from smtp SEND to reception.