string connectionString = ConfigurationManager.ConnectionStrings["email_data"].ConnectionString;
        OleDbConnection con100 = new OleDbConnection(connectionString);
        OleDbCommand cmd100 = new OleDbCommand("select top 3 emails  from bulk_tbl", con100);
        OleDbDataAdapter da100 = new OleDbDataAdapter(cmd100);
        DataSet ds100 = new DataSet();
        da100.Fill(ds100);
        {
            for (int i = 0; i < ds100.Tables[0].Rows.Count; i++)
            //try
            {
                string all_emails = ds100.Tables[0].Rows[i][0].ToString();
                {
                    string allmail = all_emails + ";";
                    Session.Add("ad_emails",allmail);
                    Response.Write(Session["ad_emails"]);
                    send_mail();
                }
            }
        }
    }

    string sendto = Session["ad_emails"].ToString();

    MailMessage message = new MailMessage("[email protected]", sendto, "subject", "body");
    SmtpClient emailClient = new SmtpClient("mail.smtp.com");
    System.Net.NetworkCredential SMTPUserInfo = new System.Net.NetworkCredential("abc", "abc");
    emailClient.UseDefaultCredentials = true;
    emailClient.Credentials = SMTPUserInfo;
    emailClient.Send(message);