特點：
1. 支持SMTP驗證
2. 支持群發功能
3. 支持各種免費郵箱，如sohu,163等
4. 支持Win2k Server自帶的smtp服務器，即只要你聯網，配置好smtp服務器，即可本機發郵件
5. 完整的錯誤代碼，擁有Logs和HTMLlogs兩個日志功能，可以輸出詳細的服務器--客戶端交互日志
代碼如下:
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using System;
using System.Text;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Collections;

namespace Sanxing.Mail.Data
{
public class ESmtpMail
{

//內部變量
/// <summary>
/// 設置換行變量
/// </summary>
private string enter="\r\n";

/// <summary>
/// 設定語言代碼，默認設定為GB2312，如不需要可設置為""
/// </summary>
private string Charset="GB2312";

/// <summary>
/// 發件人地址
/// </summary>
private string From="";

/// <summary>
/// 發件人姓名
/// </summary>
private string FromName="";

/// <summary>
/// 回復郵件地址
/// </summary>
//public string ReplyTo="";

/// <summary>
/// 收件人姓名
/// </summary>
private string RecipientName="";

/// <summary>
/// 收件人列表
/// </summary>
private Hashtable Recipient=new Hashtable();

/// <summary>
/// 郵件服務器域名
/// </summary>
private string mailserver="";

/// <summary>
/// 郵件服務器端口號
/// </summary>
private int mailserverport=25;

/// <summary>
/// SMTP認證時使用的用戶名
/// </summary>
private string username="";

/// <summary>
/// SMTP認證時使用的密碼
/// </summary>
private string password="";

/// <summary>
/// 是否需要SMTP驗證
/// </summary> 
private bool ESmtp=false;

/// <summary>
/// 是否Html郵件
/// </summary> 
private bool Html=false;

/// <summary>
/// 郵件附件列表
/// </summary>
private System.Collections.ArrayList Attachments;

/// <summary>
/// 郵件發送優先級，可設置為"High","Normal","Low"或"1","3","5"
/// </summary>
private string priority="Normal";

/// <summary>
/// 郵件主題
/// </summary> 
private string Subject="";

/// <summary>
/// 郵件正文
/// </summary> 
private string Body="";

/// <summary>
/// 收件人數量
/// </summary>
private int RecipientNum=0;

/// <summary>
/// 最多收件人數量
/// </summary>
private int recipientmaxnum=1;

/// <summary>
/// 密件收件人數量
/// </summary>
//private int RecipientBCCNum=0;

/// <summary>
/// 錯誤消息反饋
/// </summary>
private string errmsg;

/// <summary>
/// TcpClient對象，用于連接服務器
/// </summary>
private TcpClient tc;

/// <summary>
/// NetworkStream對象
/// </summary>
private NetworkStream ns;

/// <summary>
/// SMTP錯誤代碼哈希表
/// </summary>
private Hashtable ErrCodeHT = new Hashtable();

/// <summary>
/// SMTP正確代碼哈希表
/// </summary>
private Hashtable RightCodeHT = new Hashtable();

/// <summary>
/// 服務器交互記錄
/// </summary>
private string logs="";

///<summary>
///HTML格式的服務器交互記錄
///</summary>
private string htmllog="";

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代碼第一部分完畢