best way to send bulk mail in C#

public void Messager(string MessagingSubjectLine, string MessageContent, string To, string From, string SMTP)
{
    string conn = SMTP;//eg: mail.mydomain.com
    conn = conn.Split(new char[] { '=', ';' })[1];
    MailMessage varHTMLMail=new MailMessage();
    if (To.Split(';').Length > 1)
    {
        string[] amto = To.Split(';');
        foreach (string s in amto)
            varHTMLMail.To.Add(s);
    }
    else
        varHTMLMail.To.Add(To);//Used "To" here, change if you want bcc....

    varHTMLMail.From = new MailAddress(From);
    SmtpClient varSMTPClient;
    
    varHTMLMail.Subject = MessagingSubjectLine;
    varHTMLMail.Body = MessageContent;
    varHTMLMail.Priority = MailPriority.Normal;
    varHTMLMail.IsBodyHtml = true;

    varSMTPClient = new SmtpClient(conn);
    varSMTPClient.UseDefaultCredentials = true;
    varSMTPClient.Timeout = 100000 * 6;
    varSMTPClient.Send(varHTMLMail);
}