C#實現電子郵件的發送

1 引言

電子郵件介紹

電子郵件(簡稱E-mail)又稱電子信箱、電子郵政，它是一種用電子手段提供信息交換的通信方式。它是全球多種網絡上使用最普遍的一項服務。這種非交互式的通信,加速了信息的交流及數據傳送,它是一個簡易、快速的方法。通過連接全世界的Internet,實現各類信號的傳送、接收、存貯等處理,將郵件送到世界的各個角落。到目前爲止,可以說電子郵件是Internet資源使用最多的一種服務，E-mai1不只侷限於信件的傳遞,還可用來傳遞文件、聲音及圖形、圖像等不同類型的信息。

電子郵件不是一種“終端到終端”的服務,是被稱爲“存貯轉發式”服務。這正是電子信箱系統的核心，利用存貯轉發可進行非實時通信，屬異步通信方式。即信件發送者可隨時隨地發送郵件，不要求接收者同時在場，即使對方現在不在，仍可將郵件立刻送到對方的信箱內,且存儲在對方的電子郵箱中。接收者可在他認爲方便的時候讀取信件,不受時空限制。在這裏,“發送”郵件意味着將郵件放到收件人的信箱中,而“接收”郵件則意味着從自己的信箱中讀取信件,信箱實際上是由文件管理系統支持的一個實體。因爲電子郵件是通過郵件服務器(mai1server)來傳遞檔的。通常mailserver是執行多任務操作系統UNIX的計算機，它提供24小時的電子郵件服務,用戶只要向 mail server管理人員申請一個信箱賬號,就可使用這項快速的郵件服務。

電子郵件的工作原理：

• 電子郵件系統是一種新型的信息系統,是通信技術和計算機技術結合的產物。電子郵件的傳輸是通過電子郵件簡單傳輸協議(Simple Mail Transfer Protocol,簡稱SMTP)這一系統軟件來完成的,它是Internet下的一種電子郵件通信協議。
• 電子郵件的基本原理,是在通信網上設立“電子信箱系統”，它實際上是一個計算機系統。系統的硬件是一個高性能、大容量的計算機。硬盤作爲信箱的存儲介質,在硬盤上爲用戶分一定的存儲空間作爲用戶的“信箱”，每位用戶都有屬於自己的—個電子信箱。並確定—個用戶名和用戶可以自己隨意修改的口令。存儲空間包含存放所收信件、編輯信件以及信件存盤三部分空間,用戶使用口令開啓自己的信箱,並進行發信、讀信、編輯、轉發、存檔等各種操作。系統功能主要由軟件實現。
• 電子郵件的通信是在信箱之間進行的。用戶首先開啓自己的信箱，然後通過鍵入命令的方式將需要發送的郵件發到對方的信箱中。郵件在信箱之間進行傳遞和交換,也可以與另—個郵件系統進行傳遞和交換。收方在取信時，使用特定賬號從信箱提取。

2 代碼實現部分

2.1 新建郵件幫助類，自由命名即可，這裏以Utilities_Xofly爲例

郵件幫助類也可以在這裏查看：http://tool.sufeinet.com/CodePreview/CodeView.aspx?action=view&file=Mail/SmtpServerHelper.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Mail;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;
using System.Collections;

namespace Sea.Common
{
    public class Utilities_Xofly
    {
        public enum MailFormat { Text, HTML };
        public enum MailPriority { Low = 1, Normal = 3, High = 5 };

        /// <summary>  
        /// 添加附件  
        /// </summary>  
        public class MailAttachments
        {
            #region 構造函數  
            public MailAttachments()
            {
                _Attachments = new ArrayList();
            }
            #endregion

            #region 私有字段  
            private IList _Attachments;
            private const int MaxAttachmentNum = 10;
            #endregion

            #region 索引器  
            public string this[int index]
            {
                get { return (string)_Attachments[index]; }
            }
            #endregion

            #region 公共方法  
            /// <summary>  
            /// 添加郵件附件  
            /// </summary>  
            /// <param name="FilePath">附件的絕對路徑</param>  
            public void Add(params string[] filePath)
            {
                if (filePath == null)
                {
                    throw (new ArgumentNullException("非法的附件"));
                }
                else
                {
                    for (int i = 0; i < filePath.Length; i++)
                    {
                        Add(filePath[i]);
                    }
                }
            }

            /// <summary>  
            /// 添加一個附件,當指定的附件不存在時，忽略該附件，不產生異常。  
            /// </summary>  
            /// <param name="filePath">附件的絕對路徑</param>  
            public void Add(string filePath)
            {
                if (System.IO.File.Exists(filePath))
                {
                    if (_Attachments.Count < MaxAttachmentNum)
                    {
                        _Attachments.Add(filePath);
                    }
                }
            }

            /// <summary>  
            /// 清除所有附件  
            /// </summary>  
            public void Clear()
            {
                _Attachments.Clear();
            }

            /// <summary>  
            /// 獲取附件個數  
            /// </summary>  
            public int Count
            {
                get { return _Attachments.Count; }
            }
            #endregion
        }

        /// <summary>  
        /// 郵件信息  
        /// </summary>  
        public class MailMessage
        {
            #region 構造函數  
            public MailMessage()
            {
                _Recipients = new ArrayList();        //收件人列表  
                _Attachments = new MailAttachments(); //附件  
                _BodyFormat = MailFormat.HTML;        //缺省的郵件格式爲HTML  
                _Priority = MailPriority.Normal;
                _Charset = "GB2312";
            }
            #endregion

            #region 私有字段  
            private int _MaxRecipientNum = 30;
            private string _From;      //發件人地址  
            private string _FromName;  //發件人姓名  
            private IList _Recipients; //收件人  
            private MailAttachments _Attachments;//附件  
            private string _Body;      //內容  
            private string _Subject;   //主題  
            private MailFormat _BodyFormat;     //郵件格式  
            private string _Charset = "GB2312"; //字符編碼格式  
            private MailPriority _Priority;     //郵件優先級  
            #endregion

            #region 公有屬性  
            /// <summary>  
            /// 設定語言代碼，默認設定爲GB2312，如不需要可設置爲""  
            /// </summary>  
            public string Charset
            {
                get { return _Charset; }
                set { _Charset = value; }
            }

            /// <summary>  
            /// 最大收件人  
            /// </summary>  
            public int MaxRecipientNum
            {
                get { return _MaxRecipientNum; }
                set { _MaxRecipientNum = value; }
            }

            /// <summary>  
            /// 發件人地址  
            /// </summary>  
            public string From
            {
                get { return _From; }
                set { _From = value; }
            }

            /// <summary>  
            /// 發件人姓名  
            /// </summary>  
            public string FromName
            {
                get { return _FromName; }
                set { _FromName = value; }
            }

            /// <summary>  
            /// 內容  
            /// </summary>  
            public string Body
            {
                get { return _Body; }
                set { _Body = value; }
            }

            /// <summary>  
            /// 主題  
            /// </summary>  
            public string Subject
            {
                get { return _Subject; }
                set { _Subject = value; }
            }

            /// <summary>  
            /// 附件  
            /// </summary>  
            public MailAttachments Attachments
            {
                get { return _Attachments; }
                set { _Attachments = value; }
            }

            /// <summary>  
            /// 優先權  
            /// </summary>  
            public MailPriority Priority
            {
                get { return _Priority; }
                set { _Priority = value; }
            }

            /// <summary>  
            /// 收件人  
            /// </summary>  
            public IList Recipients
            {
                get { return _Recipients; }
            }

            /// <summary>  
            /// 郵件格式  
            /// </summary>  
            public MailFormat BodyFormat
            {
                set { _BodyFormat = value; }
                get { return _BodyFormat; }
            }
            #endregion

            #region 公共方法  
            /// <summary>  
            /// 增加一個收件人地址  
            /// </summary>  
            /// <param name="recipient">收件人的Email地址</param>  
            public void AddRecipients(string recipient)
            {
                if (_Recipients.Count < MaxRecipientNum)
                {
                    _Recipients.Add(recipient);
                }
            }

            /// <summary>  
            /// 增加多個收件人地址  
            /// </summary>  
            /// <param name="recipient">收件人的Email地址集合</param>  
            public void AddRecipients(params string[] recipient)
            {
                if (recipient == null)
                {
                    throw (new ArgumentException("收件人不能爲空."));
                }
                else
                {
                    for (int i = 0; i < recipient.Length; i++)
                    {
                        AddRecipients(recipient[i]);
                    }
                }
            }
            #endregion
        }

        /// <summary>  
        /// 郵件操作  
        /// </summary>  
        public class SmtpServerHelper
        {
            #region 構造函數、析構函數  
            public SmtpServerHelper()
            {
                SMTPCodeAdd();
            }

            ~SmtpServerHelper()
            {
                networkStream.Close();
                tcpClient.Close();
            }
            #endregion

            #region 私有字段  
            /// <summary>  
            /// 回車換行  
            /// </summary>  
            private string CRLF = "\r\n";

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

            /// <summary>  
            /// TcpClient對象，用於連接服務器  
            /// </summary>   
            private TcpClient tcpClient;

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

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

            /// <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();
            #endregion

            #region 公有屬性  
            /// <summary>  
            /// 錯誤消息反饋  
            /// </summary>  
            public string ErrMsg
            {
                set { errmsg = value; }
                get { return errmsg; }
            }
            #endregion

            #region 私有方法  
            /// <summary>  
            /// 將字符串編碼爲Base64字符串  
            /// </summary>  
            /// <param name="str">要編碼的字符串</param>  
            private string Base64Encode(string str)
            {
                byte[] barray;
                barray = Encoding.Default.GetBytes(str);
                return Convert.ToBase64String(barray);
            }

            /// <summary>  
            /// 將Base64字符串解碼爲普通字符串  
            /// </summary>  
            /// <param name="str">要解碼的字符串</param>  
            private string Base64Decode(string str)
            {
                byte[] barray;
                barray = Convert.FromBase64String(str);
                return Encoding.Default.GetString(barray);
            }

            /// <summary>  
            /// 得到上傳附件的文件流  
            /// </summary>  
            /// <param name="FilePath">附件的絕對路徑</param>  
            private string GetStream(string FilePath)
            {
                System.IO.FileStream FileStr = new System.IO.FileStream(FilePath, System.IO.FileMode.Open);
                byte[] by = new byte[System.Convert.ToInt32(FileStr.Length)];
                FileStr.Read(by, 0, by.Length);
                FileStr.Close();
                return (System.Convert.ToBase64String(by));
            }

            /// <summary>  
            /// SMTP迴應代碼哈希表  
            /// </summary>  
            private void SMTPCodeAdd()
            {
                ErrCodeHT.Add("421", "服務未就緒，關閉傳輸信道");
                ErrCodeHT.Add("432", "需要一個密碼轉換");
                ErrCodeHT.Add("450", "要求的郵件操作未完成，郵箱不可用（例如，郵箱忙）");
                ErrCodeHT.Add("451", "放棄要求的操作；處理過程中出錯");
                ErrCodeHT.Add("452", "系統存儲不足，要求的操作未執行");
                ErrCodeHT.Add("454", "臨時認證失敗");
                ErrCodeHT.Add("500", "郵箱地址錯誤");
                ErrCodeHT.Add("501", "參數格式錯誤");
                ErrCodeHT.Add("502", "命令不可實現");
                ErrCodeHT.Add("503", "服務器需要SMTP驗證");
                ErrCodeHT.Add("504", "命令參數不可實現");
                ErrCodeHT.Add("530", "需要認證");
                ErrCodeHT.Add("534", "認證機制過於簡單");
                ErrCodeHT.Add("538", "當前請求的認證機制需要加密");
                ErrCodeHT.Add("550", "要求的郵件操作未完成，郵箱不可用（例如，郵箱未找到，或不可訪問）");
                ErrCodeHT.Add("551", "用戶非本地，請嘗試<forward-path>");
                ErrCodeHT.Add("552", "過量的存儲分配，要求的操作未執行");
                ErrCodeHT.Add("553", "郵箱名不可用，要求的操作未執行（例如郵箱格式錯誤）");
                ErrCodeHT.Add("554", "傳輸失敗");

                RightCodeHT.Add("220", "服務就緒");
                RightCodeHT.Add("221", "服務關閉傳輸信道");
                RightCodeHT.Add("235", "驗證成功");
                RightCodeHT.Add("250", "要求的郵件操作完成");
                RightCodeHT.Add("251", "非本地用戶，將轉發向<forward-path>");
                RightCodeHT.Add("334", "服務器響應驗證Base64字符串");
                RightCodeHT.Add("354", "開始郵件輸入，以<CRLF>.<CRLF>結束");
            }

            /// <summary>  
            /// 發送SMTP命令  
            /// </summary>   
            private bool SendCommand(string str)
            {
                byte[] WriteBuffer;
                if (str == null || str.Trim() == String.Empty)
                {
                    return true;
                }
                logs += str;
                WriteBuffer = Encoding.Default.GetBytes(str);
                try
                {
                    networkStream.Write(WriteBuffer, 0, WriteBuffer.Length);
                }
                catch
                {
                    errmsg = "網絡連接錯誤";
                    return false;
                }
                return true;
            }

            /// <summary>  
            /// 接收SMTP服務器迴應  
            /// </summary>  
            private string RecvResponse()
            {
                int StreamSize;
                string Returnvalue = String.Empty;
                byte[] ReadBuffer = new byte[1024];
                try
                {
                    StreamSize = networkStream.Read(ReadBuffer, 0, ReadBuffer.Length);
                }
                catch
                {
                    errmsg = "網絡連接錯誤";
                    return "false";
                }

                if (StreamSize == 0)
                {
                    return Returnvalue;
                }
                else
                {
                    Returnvalue = Encoding.Default.GetString(ReadBuffer).Substring(0, StreamSize);
                    logs += Returnvalue + this.CRLF;
                    return Returnvalue;
                }
            }

            /// <summary>  
            /// 與服務器交互，發送一條命令並接收回應。  
            /// </summary>  
            /// <param name="str">一個要發送的命令</param>  
            /// <param name="errstr">如果錯誤，要反饋的信息</param>  
            private bool Dialog(string str, string errstr)
            {
                if (str == null || str.Trim() == string.Empty)
                {
                    return true;
                }
                if (SendCommand(str))
                {
                    string RR = RecvResponse();
                    if (RR == "false")
                    {
                        return false;
                    }

                    //檢查返回的代碼，根據[RFC 821]返回代碼爲3位數字代碼如220  
                    string RRCode = RR.Substring(0, 3);
                    if (RightCodeHT[RRCode] != null)
                    {
                        return true;
                    }
                    else
                    {
                        if (ErrCodeHT[RRCode] != null)
                        {
                            errmsg += (RRCode + ErrCodeHT[RRCode].ToString());
                            errmsg += CRLF;
                        }
                        else
                        {
                            errmsg += RR;
                        }
                        errmsg += errstr;
                        return false;
                    }
                }
                else
                {
                    return false;
                }
            }

            /// <summary>  
            /// 與服務器交互，發送一組命令並接收回應。  
            /// </summary>  
            private bool Dialog(string[] str, string errstr)
            {
                for (int i = 0; i < str.Length; i++)
                {
                    if (!Dialog(str[i], ""))
                    {
                        errmsg += CRLF;
                        errmsg += errstr;
                        return false;
                    }
                }
                return true;
            }

            /// <summary>  
            /// 連接服務器  
            /// </summary>  
            private bool Connect(string smtpServer, int port)
            {
                try
                {
                    tcpClient = new TcpClient(smtpServer, port);
                }
                catch (Exception e)
                {
                    errmsg = e.ToString();
                    return false;
                }
                networkStream = tcpClient.GetStream();

                if (RightCodeHT[RecvResponse().Substring(0, 3)] == null)
                {
                    errmsg = "網絡連接失敗";
                    return false;
                }
                return true;
            }

            /// <summary>  
            /// 獲取優先級  
            /// </summary>  
            /// <param name="mailPriority">優先級</param>  
            private string GetPriorityString(MailPriority mailPriority)
            {
                string priority = "Normal";
                if (mailPriority == MailPriority.Low)
                {
                    priority = "Low";
                }
                else if (mailPriority == MailPriority.High)
                {
                    priority = "High";
                }
                return priority;
            }

            /// <summary>  
            /// 發送電子郵件  
            /// </summary>  
            /// <param name="smtpServer">發信SMTP服務器</param>  
            /// <param name="port">端口，默認爲25</param>  
            /// <param name="username">發信人郵箱地址</param>  
            /// <param name="password">發信人郵箱密碼</param>  
            /// <param name="mailMessage">郵件內容</param>  
            private bool SendEmail(string smtpServer, int port, bool ESmtp, string username, string password, MailMessage mailMessage)
            {
                if (Connect(smtpServer, port) == false) return false;

                string priority = GetPriorityString(mailMessage.Priority);

                bool Html = (mailMessage.BodyFormat == MailFormat.HTML);

                string[] SendBuffer;
                string SendBufferstr;

                //進行SMTP驗證  
                if (ESmtp)
                {
                    SendBuffer = new String[4];
                    SendBuffer[0] = "EHLO " + smtpServer + CRLF;
                    SendBuffer[1] = "AUTH LOGIN" + CRLF;
                    SendBuffer[2] = Base64Encode(username) + CRLF;
                    SendBuffer[3] = Base64Encode(password) + CRLF;
                    if (!Dialog(SendBuffer, "SMTP服務器驗證失敗，請覈對用戶名和密碼。")) return false;
                }
                else
                {
                    SendBufferstr = "HELO " + smtpServer + CRLF;
                    if (!Dialog(SendBufferstr, "")) return false;
                }

                //發件人地址  
                SendBufferstr = "MAIL FROM:<" + username + ">" + CRLF;
                if (!Dialog(SendBufferstr, "發件人地址錯誤，或不能爲空")) return false;

                //收件人地址  
                SendBuffer = new string[mailMessage.Recipients.Count];
                for (int i = 0; i < mailMessage.Recipients.Count; i++)
                {
                    SendBuffer[i] = "RCPT TO:<" + (string)mailMessage.Recipients[i] + ">" + CRLF;
                }
                if (!Dialog(SendBuffer, "收件人地址有誤")) return false;

                SendBufferstr = "DATA" + CRLF;
                if (!Dialog(SendBufferstr, "")) return false;

                //發件人姓名  
                SendBufferstr = "From:" + mailMessage.FromName + "<" + mailMessage.From + ">" + CRLF;

                if (mailMessage.Recipients.Count == 0)
                {
                    return false;
                }
                else
                {
                    SendBufferstr += "To:=?" + mailMessage.Charset.ToUpper() + "?B?" + Base64Encode((string)mailMessage.Recipients[0]) + "?=" + "<" + (string)mailMessage.Recipients[0] + ">" + CRLF;
                }
                SendBufferstr += ((mailMessage.Subject == String.Empty || mailMessage.Subject == null) ? "Subject:" : ((mailMessage.Charset == "") ? ("Subject:" + mailMessage.Subject) : ("Subject:" + "=?" + mailMessage.Charset.ToUpper() + "?B?" + Base64Encode(mailMessage.Subject) + "?="))) + CRLF;
                SendBufferstr += "X-Priority:" + priority + CRLF;
                SendBufferstr += "X-MSMail-Priority:" + priority + CRLF;
                SendBufferstr += "Importance:" + priority + CRLF;
                SendBufferstr += "X-Mailer: Lion.Web.Mail.SmtpMail Pubclass [cn]" + CRLF;
                SendBufferstr += "MIME-Version: 1.0" + CRLF;
                if (mailMessage.Attachments.Count != 0)
                {
                    SendBufferstr += "Content-Type: multipart/mixed;" + CRLF;
                    SendBufferstr += " boundary=\"=====" + (Html ? "001_Dragon520636771063_" : "001_Dragon303406132050_") + "=====\"" + CRLF + CRLF;
                }
                if (Html)
                {
                    if (mailMessage.Attachments.Count == 0)
                    {
                        SendBufferstr += "Content-Type: multipart/alternative;" + CRLF; //內容格式和分隔符  
                        SendBufferstr += " boundary=\"=====003_Dragon520636771063_=====\"" + CRLF + CRLF;
                        SendBufferstr += "This is a multi-part message in MIME format." + CRLF + CRLF;
                    }
                    else
                    {
                        SendBufferstr += "This is a multi-part message in MIME format." + CRLF + CRLF;
                        SendBufferstr += "--=====001_Dragon520636771063_=====" + CRLF;
                        SendBufferstr += "Content-Type: multipart/alternative;" + CRLF; //內容格式和分隔符  
                        SendBufferstr += " boundary=\"=====003_Dragon520636771063_=====\"" + CRLF + CRLF;
                    }
                    SendBufferstr += "--=====003_Dragon520636771063_=====" + CRLF;
                    SendBufferstr += "Content-Type: text/plain;" + CRLF;
                    SendBufferstr += ((mailMessage.Charset == "") ? (" charset=\"iso-8859-1\"") : (" charset=\"" + mailMessage.Charset.ToLower() + "\"")) + CRLF;
                    SendBufferstr += "Content-Transfer-Encoding: base64" + CRLF + CRLF;
                    SendBufferstr += Base64Encode("郵件內容爲HTML格式，請選擇HTML方式查看") + CRLF + CRLF;

                    SendBufferstr += "--=====003_Dragon520636771063_=====" + CRLF;

                    SendBufferstr += "Content-Type: text/html;" + CRLF;
                    SendBufferstr += ((mailMessage.Charset == "") ? (" charset=\"iso-8859-1\"") : (" charset=\"" + mailMessage.Charset.ToLower() + "\"")) + CRLF;
                    SendBufferstr += "Content-Transfer-Encoding: base64" + CRLF + CRLF;
                    SendBufferstr += Base64Encode(mailMessage.Body) + CRLF + CRLF;
                    SendBufferstr += "--=====003_Dragon520636771063_=====--" + CRLF;
                }
                else
                {
                    if (mailMessage.Attachments.Count != 0)
                    {
                        SendBufferstr += "--=====001_Dragon303406132050_=====" + CRLF;
                    }
                    SendBufferstr += "Content-Type: text/plain;" + CRLF;
                    SendBufferstr += ((mailMessage.Charset == "") ? (" charset=\"iso-8859-1\"") : (" charset=\"" + mailMessage.Charset.ToLower() + "\"")) + CRLF;
                    SendBufferstr += "Content-Transfer-Encoding: base64" + CRLF + CRLF;
                    SendBufferstr += Base64Encode(mailMessage.Body) + CRLF;
                }
                if (mailMessage.Attachments.Count != 0)
                {
                    for (int i = 0; i < mailMessage.Attachments.Count; i++)
                    {
                        string filepath = (string)mailMessage.Attachments[i];
                        SendBufferstr += "--=====" + (Html ? "001_Dragon520636771063_" : "001_Dragon303406132050_") + "=====" + CRLF;
                        SendBufferstr += "Content-Type: text/plain;" + CRLF;
                        SendBufferstr += " name=\"=?" + mailMessage.Charset.ToUpper() + "?B?" + Base64Encode(filepath.Substring(filepath.LastIndexOf("\\") + 1)) + "?=\"" + CRLF;
                        SendBufferstr += "Content-Transfer-Encoding: base64" + CRLF;
                        SendBufferstr += "Content-Disposition: attachment;" + CRLF;
                        SendBufferstr += " filename=\"=?" + mailMessage.Charset.ToUpper() + "?B?" + Base64Encode(filepath.Substring(filepath.LastIndexOf("\\") + 1)) + "?=\"" + CRLF + CRLF;
                        SendBufferstr += GetStream(filepath) + CRLF + CRLF;
                    }
                    SendBufferstr += "--=====" + (Html ? "001_Dragon520636771063_" : "001_Dragon303406132050_") + "=====--" + CRLF + CRLF;
                }
                SendBufferstr += CRLF + "." + CRLF;
                if (!Dialog(SendBufferstr, "錯誤信件信息")) return false;

                SendBufferstr = "QUIT" + CRLF;
                if (!Dialog(SendBufferstr, "斷開連接時錯誤")) return false;

                networkStream.Close();
                tcpClient.Close();
                return true;
            }
            #endregion

            #region 公有方法  
            /// <summary>  
            /// 發送電子郵件,SMTP服務器不需要身份驗證  
            /// </summary>  
            /// <param name="smtpServer">發信SMTP服務器</param>  
            /// <param name="port">端口，默認爲25</param>  
            /// <param name="mailMessage">郵件內容</param>  
            public bool SendEmail(string smtpServer, int port, MailMessage mailMessage)
            {
                return SendEmail(smtpServer, port, false, "", "", mailMessage);
            }

            /// <summary>  
            /// 發送電子郵件,SMTP服務器需要身份驗證  
            /// </summary>  
            /// <param name="smtpServer">發信SMTP服務器</param>  
            /// <param name="port">端口，默認爲25</param>  
            /// <param name="username">發信人郵箱地址</param>  
            /// <param name="password">發信人郵箱密碼</param>  
            /// <param name="mailMessage">郵件內容</param>  
            public bool SendEmail(string smtpServer, int port, string username, string password, MailMessage mailMessage)
            {
                return SendEmail(smtpServer, port, true, username, password, mailMessage);
            }
            #endregion
        }

        /// <summary>  
        /// 發送郵件  
        /// </summary>  
        //--------------------調用-----------------------  
        //MailAttachments ma=new MailAttachments();  
        //ma.Add(@"附件地址");  
        //MailMessage mail = new MailMessage();  
        //mail.Attachments=ma;  
        //mail.Body="你好";  
        //mail.AddRecipients("[email protected]");  
        //mail.From="[email protected]";  
        //mail.FromName="zjy";  
        //mail.Subject="Hello";  
        //SmtpClient sp = new SmtpClient();  
        //sp.SmtpServer = "smtp.163.com";  
        //sp.Send(mail, "[email protected]", "123456");  
        //------------------------------------------------  
        public class SmtpClient
        {
            #region 構造函數  
            public SmtpClient()
            { }

            public SmtpClient(string _smtpServer)
            {
                _SmtpServer = _smtpServer;
            }
            #endregion

            #region 私有字段  
            private string errmsg;
            private string _SmtpServer;
            #endregion

            #region 公有屬性  
            /// <summary>  
            /// 錯誤消息反饋  
            /// </summary>  
            public string ErrMsg
            {
                get { return errmsg; }
            }

            /// <summary>  
            /// 郵件服務器  
            /// </summary>  
            public string SmtpServer
            {
                set { _SmtpServer = value; }
                get { return _SmtpServer; }
            }
            #endregion

            public bool Send(MailMessage mailMessage, string username, string password)
            {
                SmtpServerHelper helper = new SmtpServerHelper();
                if (helper.SendEmail(_SmtpServer, 25, username, password, mailMessage))
                    return true;
                else
                {
                    errmsg = helper.ErrMsg;
                    return false;
                }
            }
        }

        /// <summary>  
        /// 操作服務器上郵件  
        /// </summary>  
        public class SmtpMail
        {
            public SmtpMail()
            { }

            #region 字段  
            private StreamReader sr;
            private StreamWriter sw;
            private TcpClient tcpClient;
            private NetworkStream networkStream;
            #endregion

            #region 私有方法  
            /// <summary>  
            /// 向服務器發送信息  
            /// </summary>  
            private bool SendDataToServer(string str)
            {
                try
                {
                    sw.WriteLine(str);
                    sw.Flush();
                    return true;
                }
                catch (Exception err)
                {
                    return false;
                }
            }

            /// <summary>  
            /// 從網絡流中讀取服務器回送的信息  
            /// </summary>  
            private string ReadDataFromServer()
            {
                string str = null;
                try
                {
                    str = sr.ReadLine();
                    if (str[0] == '-')
                    {
                        str = null;
                    }
                }
                catch (Exception err)
                {
                    str = err.Message;
                }
                return str;
            }
            #endregion

            #region 獲取郵件信息  
            /// <summary>  
            /// 獲取郵件信息  
            /// </summary>  
            /// <param name="uid">郵箱賬號</param>  
            /// <param name="pwd">郵箱密碼</param>  
            /// <returns>郵件信息</returns>  
            public ArrayList ReceiveMail(string uid, string pwd)
            {
                ArrayList EmailMes = new ArrayList();
                string str;
                int index = uid.IndexOf('@');
                string pop3Server = "pop3." + uid.Substring(index + 1);
                tcpClient = new TcpClient(pop3Server, 110);
                networkStream = tcpClient.GetStream();
                sr = new StreamReader(networkStream);
                sw = new StreamWriter(networkStream);

                if (ReadDataFromServer() == null) return EmailMes;
                if (SendDataToServer("USER " + uid) == false) return EmailMes;
                if (ReadDataFromServer() == null) return EmailMes;
                if (SendDataToServer("PASS " + pwd) == false) return EmailMes;
                if (ReadDataFromServer() == null) return EmailMes;
                if (SendDataToServer("LIST") == false) return EmailMes;
                if ((str = ReadDataFromServer()) == null) return EmailMes;

                string[] splitString = str.Split(' ');
                int count = int.Parse(splitString[1]);
                if (count > 0)
                {
                    for (int i = 0; i < count; i++)
                    {
                        if ((str = ReadDataFromServer()) == null) return EmailMes;
                        splitString = str.Split(' ');
                        EmailMes.Add(string.Format("第{0}封郵件，{1}字節", splitString[0], splitString[1]));
                    }
                    return EmailMes;
                }
                else
                {
                    return EmailMes;
                }
            }
            #endregion

            #region 讀取郵件內容  
            /// <summary>  
            /// 讀取郵件內容  
            /// </summary>  
            /// <param name="mailMessage">第幾封</param>  
            /// <returns>內容</returns>  
            public string ReadEmail(string str)
            {
                string state = "";
                if (SendDataToServer("RETR " + str) == false)
                    state = "Error";
                else
                {
                    state = sr.ReadToEnd();
                }
                return state;
            }
            #endregion

            #region 刪除郵件  
            /// <summary>  
            /// 刪除郵件  
            /// </summary>  
            /// <param name="str">第幾封</param>  
            /// <returns>操作信息</returns>  
            public string DeleteEmail(string str)
            {
                string state = "";
                if (SendDataToServer("DELE " + str) == true)
                {
                    state = "成功刪除";
                }
                else
                {
                    state = "Error";
                }
                return state;
            }
            #endregion

            #region 關閉服務器連接  
            /// <summary>  
            /// 關閉服務器連接  
            /// </summary>  
            public void CloseConnection()
            {
                SendDataToServer("QUIT");
                sr.Close();
                sw.Close();
                networkStream.Close();
                tcpClient.Close();
            }
            #endregion
        }

    }
}

2.2 方法的調用

方法調用查看如下所示的樣例，mail.AddRecipients()方法，如果需要發送多個郵箱的時候傳入數組即可。

        /// <summary>  
        /// 發送郵件  
        /// </summary>  
        //--------------------調用-----------------------  
        //MailAttachments ma=new MailAttachments();  
        //ma.Add(@"附件地址");  
        //MailMessage mail = new MailMessage();  
        //mail.Attachments=ma;  
        //mail.Body="你好";  
        //mail.AddRecipients("[email protected]");  
        //mail.From="[email protected]";  
        //mail.FromName="zjy";  
        //mail.Subject="Hello";  
        //SmtpClient sp = new SmtpClient();  
        //sp.SmtpServer = "smtp.163.com";  
        //sp.Send(mail, "[email protected]", "123456");  
        //------------------------------------------------  

2.3 查看相關郵箱的設置（這裏以QQ郵箱爲例）

點擊查看POP3/SMTP服務，記得一定要開啓哦，開啓之後如下圖所示。

2.4 運行相關程序，查看郵件內容是否正確

郵件發送成功之後登錄到對應的接收郵箱查看郵件內容是否正確。