邮件有需要加密的地方，提供一个加密方法类

public static class DesSet

{

    /// <summary>

    /// 加密方法 Key 必须为8位

    /// </summary>

    /// <param name="pToEncrypt"></param>

    /// <param name="sKey"></param>

    /// <returns></returns>

    public static string Encrypt(string pToEncrypt, string sKey)

    {

        DESCryptoServiceProvider des = new DESCryptoServiceProvider();

        byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);

        des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);

        des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

        MemoryStream ms = new MemoryStream();

        CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);

        cs.Write(inputByteArray, 0, inputByteArray.Length);

        cs.FlushFinalBlock();

        StringBuilder ret = new StringBuilder();

        foreach (byte b in ms.ToArray())

        {

            ret.AppendFormat("{0:X2}", b);

        }

        ret.ToString();

        return ret.ToString();

    }

    /// <summary>

    /// 解密方法 Key 必须为8位

    /// </summary>

    /// <param name="pToDecrypt"></param>

    /// <param name="sKey"></param>

    /// <returns></returns>

    public static string Decrypt(string pToDecrypt, string sKey)

    {

        try

        {

            DESCryptoServiceProvider des = new DESCryptoServiceProvider();

            byte[] inputByteArray = new byte[pToDecrypt.Length / 2];

            for (int x = 0; x < pToDecrypt.Length / 2; x++)

            {

                int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));

                inputByteArray[x] = (byte)i;

            }

            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);

            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

            MemoryStream ms = new MemoryStream();

            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);

            cs.Write(inputByteArray, 0, inputByteArray.Length);

            //如果数据为空字符串会报不正确的数据

            cs.FlushFinalBlock();

            StringBuilder ret = new StringBuilder();

            return System.Text.Encoding.Default.GetString(ms.ToArray());

        }

        catch

        {

            return null;

        }

    }

    /// <summary>

    /// 解密方法 Key 必须为8位

    /// </summary>

    /// <param name="pToDecrypt"></param>

    /// <param name="sKey"></param>

    /// <returns></returns>

    public static string qxDecrypt(string pToDecrypt, string sKey)

    {

        DESCryptoServiceProvider des = new DESCryptoServiceProvider();

        byte[] inputByteArray = new byte[pToDecrypt.Length / 2];

        for (int x = 0; x < pToDecrypt.Length / 2; x++)

        {

            int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));

            inputByteArray[x] = (byte)i;

        }

        des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);

        des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

        MemoryStream ms = new MemoryStream();

        CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);

        cs.Write(inputByteArray, 0, inputByteArray.Length);

        //如果数据为空字符串会报不正确的数据

        cs.FlushFinalBlock();

        StringBuilder ret = new StringBuilder();

        return System.Text.Encoding.Default.GetString(ms.ToArray());

    }

}

********************************************************************************

群发上千封邮件，发送太快，会出现可能被服务器拒绝的情况。使用线程控制发送间隔

    protected void btn_sendMail_Click(object sender, EventArgs e)

    {

        ThreadStart mailThread = new ThreadStart(SendMail);

        Thread sendMail = new Thread(mailThread);

        sendMail.Name = "thread send mail";

        sendMail.Start();

    }

    private void SendMail()

    {

        Mails mySendMail = new Mails();

        for (int i = 0; i < lists.Count; i++)

        {

            mySendMail = new Mails("nihao",lists[i].ToString(), lists[i]);

            mySendMail.SendMail();

            if ((i + 1) % 50 == 0)

            {

                Thread.Sleep(60000);//歇一分钟再发吧。。

            }

        }

    }

*****************************************************************

Mails类

    public void SendMail()

    {

        lock (this)

        {

            Thread.Sleep(3000);

            //创建smtpclient对象

            System.Net.Mail.SmtpClient client = new SmtpClient();

            client.Host = smtp;

            client.UseDefaultCredentials = false;

            client.Credentials = new System.Net.NetworkCredential(from,pwd);

            client.DeliveryMethod = SmtpDeliveryMethod.Network;

            //创建mailMessage对象

            System.Net.Mail.MailMessage message = new MailMessage(from,to);

            message.Subject = subject;

            message.SubjectEncoding = Encoding.UTF8;

            message.Body = body;

            message.BodyEncoding = System.Text.Encoding.UTF8;

            message.IsBodyHtml = true;

            try

            {

                client.Send(message);

                StreamWriter sw = new StreamWriter("c:/message.txt", true);

                sw.Write(this.to+"  发送成功" + "\r\n");

                sw.Close();

            }

            catch (Exception ex)

            {

                StreamWriter sw = new StreamWriter("c:/message.txt", true);

                sw.Write(this.to+"  发送失败。失败原因："+ex.Message + "\r\n");

                sw.Close();

            }

        }

    }