System.web.mail和System.Net.mail简单的邮件发送

最近在做一个发送邮件的功能，在网上找了半天，找到两个简单的发送方法，一个System.web.mail的发送方法，具体有什么区别我也没弄清楚，还要做把发送的邮件备份到已发送中去，也没搞定

 /// <summary>
    /// System.web.Mail的邮件发送方法
    /// </summary>
    /// <param name='clientHost'>邮件服务器地址</param>
    /// <param name='emailAddress'>发件人邮箱地址</param>
    /// <param name='receiveAddress'>收件人邮箱地址</param>
    /// <param name='userName'>发件人邮箱用户名</param>
    /// <param name='password'>发件人邮箱密码</param>
    /// <param name="subject">邮件主题</param>
    /// <param name="body">邮件正文</param>
    public string andEmail(string clientHost, string emailAddress, string receiveAddress,string userName, string password, string subject, string body)
    {
        System.Web.Mail.MailMessage objMailMessage;
        // MailAttachment objMailAttachment; 
        // 创建一个附件对象 
        // objMailAttachment = new MailAttachment( "d://test.txt" );//发送邮件的附件 
        // 创建邮件消息 
        objMailMessage = new System.Web.Mail.MailMessage();
        objMailMessage.From = emailAddress;//源邮件地址 
        objMailMessage.To = receiveAddress;//目的邮件地址
        objMailMessage.Subject = subject;//发送邮件的标题 
        objMailMessage.BodyFormat = MailFormat.Html;
        objMailMessage.Body = body;//发送邮件的内容 
        //  objMailMessage.Attachments.Add( objMailAttachment );//将附件附加到邮件消息对象中 
        //接着利用sina的SMTP来发送邮件，需要使用Microsoft .NET Framework SDK v1.1和它以上的版本 
        //基本权限 
        objMailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", "1");
        //用户名 
        objMailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", userName);
        //密码 
        objMailMessage.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", password);
        //如果没有上述三行代码，则出现如下错误提示：服务器拒绝了一个或多个收件人地址。服务器响应为: 554 : Client host rejected: Access denied 
        //SMTP地址 
        SmtpMail.SmtpServer = clientHost;
        try
        {
            //开始发送邮件 
            SmtpMail.Send(objMailMessage);
        }
        catch (Exception ex)
        {
            return ex.ToString();
        }
        return "成功";
    }

system.NEt 。mail的方法

    /// <summary>
    /// System.NET.Mail的邮件发送方法
    /// </summary>
    /// <param name='clientHost'>邮件服务器地址</param>
    /// <param name='emailAddress'>发件人邮箱地址</param>
    /// <param name='receiveAddress'>收件人邮箱地址</param>
    /// <param name='userName'>发件人邮箱用户名</param>
    /// <param name='password'>发件人邮箱密码</param>
    /// <param name="subject">邮件主题</param>
    /// <param name="body">邮件正文</param>
    public void SendEmail(string clientHost, string emailAddress, string receiveAddress,
        string userName, string password, string subject, string body)
    {
        System.Web.Mail.MailMessage mail = new System.Web.Mail.MailMessage();
        mail.From = new MailAddress(emailAddress);
        mail.To.Add(new MailAddress(receiveAddress));
        mail.Subject = subject;
        mail.Body = body;
        mail.IsBodyHtml = true;
        mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnSuccess;

        SmtpClient client = new SmtpClient();
        client.Host = clientHost;
        client.Credentials = new NetworkCredential(userName, password);
        client.DeliveryMethod = SmtpDeliveryMethod.Network;

        //client.UseDefaultCredentials = true;
        try
        {
            client.Send(mail);
        }
        catch (Exception ex)
        {
            Response.Write(ex);
            // Get ex.Message and do something
        }
    }