对于还没用动手写过程序的人来说，动手是必须的，只有自己动手写写程序才能在锻炼中不断提高，今天和大家一起探讨一个程序c#中邮件收发处理（POP3,IMAP,SMTP）的实现方法，程序有点长，希望大家坚持看完，看透，看明白。

本文涉及的内容：
1：自己制作Pop3Helper
   信件格式的处理有麻烦
2：使用现成的pop3类
   LumiSoft.Net.POP3.Client;
      有两种处理方法
3：使用IMAP收邮件
      功能似乎更多，比起pop3来。
4：SMTP发送邮件
   关于 Mailbox unavailable. The server response was: 5.7.1 Unable to relay for xx 的错误处理 
自己写一个POP3的接收程序并不是很简单。主要问题就是如何处理信件的格式。
其处理方法不是太复杂，用一个tcp联接就可以了。
这是代码
     public class Pop3Helper
    {
        string _pop3server;
        string _user;
        int _port;
        string _pwd;
        public TcpClient _server;
        public NetworkStream _netStream;
        public StreamReader _reader;
        public string _data;
        public byte[] _charData;
        public string _CRLF = \"\\r\\n\";
        private string _log;
        public string LogMSG
        {
            get { return _log; }
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name=\"server\"></param>
        /// <param name=\"port\"></param>
        /// <param name=\"user\"></param>
        /// <param name=\"pwd\"></param>
        public Pop3Helper(string server, int port, string user, string pwd)
        {
            _pop3server = server; [Page]
            _port = port;
            _user = user;
            _pwd = pwd;
        }
        /// <summary>
        /// connect
        /// </summary>
        public void Connect()
        {
            //create a tcp connection
            _server = new TcpClient(_pop3server, _port);
            //prepare 
            _netStream = _server.GetStream();

if (!CheckResult(_reader.ReadLine()))
                throw new Exception(\"Pass Error\"); [Page]
        }
        /// <summary>
        /// get message Numbers
        /// </summary>
        /// <returns></returns>
        public int GetMailCount()
        {
            try
            {
                _data = \"STAT\" + _CRLF;
                _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray());
                _netStream.Write(_charData, 0, _charData.Length);
                string resp = _reader.ReadLine();
                string[] tokens = resp.Split(new char[] { ’ ’ });
                return Convert.ToInt32(tokens[1]);
            }
            catch (Exception ex)
            {
                return 0;
            }
        }
        public string GetMail(int id)
        {
            string line;
            string content = \"\";
            try
            {
                //get by id
                _data = \"RETR \" + id + _CRLF;
                _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray()); [Page]
                _netStream.Write(_charData, 0, _charData.Length);
                line = _reader.ReadLine();
                if (line[0] != ’-’)
                {
                    //end with ’.’
                    while (line != \".\")
                    {
                        line = _reader.ReadLine();
                        content += line + \"\\r\\n\";
                    }
                }

return content;
            }
            catch (Exception err)
            {
                Log(err.Message);
                return \"Error\";
            }
        }

_reader = new StreamReader(_server.GetStream());
            if (!CheckResult(_reader.ReadLine()))
                throw new Exception(\"Connect Error\");
            //login
            _data = \"USER \" + this._user + _CRLF;
            _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray());
            _netStream.Write(_charData, 0, _charData.Length);
            if (!CheckResult(_reader.ReadLine()))
                throw new Exception(\"User Error\");
            _data = \"PASS \" + this._pwd + _CRLF;
            _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray());
            _netStream.Write(_charData, 0, _charData.Length);

public void DeleteMail(int id)
        {
            _data = \"DELE\" + id + _CRLF;
            _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray());
            _netStream.Write(_charData, 0, _charData.Length); [Page]
            if (!CheckResult(_reader.ReadLine()))
                throw new Exception(\"Delete Error\");
        }
        /// <summary>
        /// close connection
        /// </summary>
        public void Close()
        {
            _data = \"QUIT\" + _CRLF;
            _charData = System.Text.Encoding.ASCII.GetBytes(_data.ToCharArray());
            _netStream.Write(_charData, 0, _charData.Length);
            //close 
            _netStream.Close();
            _reader.Close();
        }
        private bool CheckResult(string reply)
        {
            Log(reply);
            if (reply.IndexOf(\"+OK\") > -1)
                return true;
            else
                return false;
        }
        private void Log(string msg)
        {
            _log += msg + \"\\r\\n\";
        }
    }
。。。。。
但是这种方式的一个问题就是关于解析信件的格式。如果是附件的话，他也直接给出了二进制，不容易使用。
所以，可以使用一个现成的工具：LumiSoft.Net.POP3.Client。这里面已经给写好了实现，用起来也很简单。
这是一个简单的用法（这里使用了两种处理方式，前一种是不建议使用的）
。。
            using (POP3_Client pop3 = new POP3_Client()) [Page]
            {
                //与Pop3服务器建立连接
                pop3.Connect(_popServer, _pop3port,false);
                //验证身份
                pop3.Authenticate(_user, _pwd, false);
                //get all messages
                POP3_MessagesInfo infos = pop3.GetMessagesInfo();
                 foreach (POP3_MessageInfo info in infos)
                {
                    byte[] bytes = pop3.GetMessage(info.MessageNumber);
                    Mime mime = Mime.Parse(bytes);
                    HandleMail(mime);
                    //delete it at last
                    //pop3.DeleteMessage(info.MessageNumber);
                }
                //the second way to do it

//for (int i = 0; i < pop3.Messages.Count; i++)
                //{
                //    byte[] bytes = pop3.Messages[i].MessageToByte();
                //    Mime mime = Mime.Parse(bytes);
                //    HandleMail(mime); [Page]
                //    //delete it at last
                //    //pop3.DeleteMessage(pop3.Messages[i].SequenceNumber);
                //}。
。。。
取得的邮件可以这要给获得。
   #region pop3
            //string customer = mime.MainEntity.To.ToAddressListString();//cargo company
            //string sender = mime.MainEntity.From.ToAddressListString();//this is customer who send
            #endregion
            string customer = MailboxesToString(envelope.To);//cargo company
            string sender = MailboxesToString(envelope.From);//this is customer who send
。。。
除此之外，它提供的另外一个工具是IMAP，它操作起来更加方便。代码如下：
。
  IMAP_Client clnt = new IMAP_Client();
            try
            {
                clnt.Connect(\"mail.xx.com\", 143, false);
                clnt.Authenticate(\"user\", \"password\");
                string[] folders = clnt.GetFolders();//get all types
                string folder = \"Inbox\";
                clnt.SelectFolder(folder);

IMAP_SequenceSet sequence_set = new IMAP_SequenceSet();
                // All messages
                sequence_set.Parse(string.Format(\"{0}:{1}\", 1, clnt.MessagesCount));
                IMAP_FetchItem[] fetchItems = clnt.FetchMessages( [Page]

}
                    catch (Exception ex)
                    {
                        Log(\"Sys\", ex.Message);
                    } [Page]
                }
                //delete it after hanlde
                clnt.DeleteMessages(sequence_set, false);
                //disconnect
                clnt.Disconnect();
                //MessageBox.Show(count.ToString() + \" of \" + fetchItems .Length+ \" Success\");
            }
            catch (Exception x)
            {
                Log(\"Sys\", x.Message);
                //MessageBox.Show(x.Message);
            }
 
。。
上边都是如何收邮件。
关于如何发送邮件是比较简单的。这里提供两种方式。
第一种方式是使用网上的smtp。这种方式必须要提供用户名和密码。这个适合于web应用，使用的smtp也是网上的，我一般使用163的smtp，基本没有问题。
第二种方式是使用本地的smtp。不需要提供密码，用户也可以是不存在的（垃圾邮件是不是就是这么产生的？），但是必要要提供smtp端口号。
第二种方法测试的时候有时候会报错“Mailbox unavailable. The server response was: 5.7.1 Unable to relay for xxx”，查过资料之后（在baidu上没找到，还是google信息多一点），才发现问题原来是IIS里SMTP服务的配置有问题。
这样修改可以解决：到开SMTP属性—>Access页面Reply Restrictions/ Reply-Only this Below选项，加上自己的ip：127.0.0.1（允许本机，使用loalhost，如果是允许其他机器，类似设置）
代码如下
public class EMail
    {
        static public string accountName;
        static public string password;
        static public string smtpServer;
        static public int smtpPort;
        /// <summary>
        /// need password,username, smtpserver
        /// </summary> [Page]
        /// <param name=\"to\"></param>
        /// <param name=\"subject\"></param>
        /// <param name=\"body\"></param>
        static public void SendMail(string sendTo, string subject, string body)
        {
            //.net smtp 
            System.Web.Mail.MailMessage mailmsg = new System.Web.Mail.MailMessage();
            mailmsg.To = sendTo;
            //mailmsg.Cc = cc;
            mailmsg.Subject = subject;
            mailmsg.Body = body;
            //sender here
            mailmsg.From = EMail.accountName; 
            // certify needed  
            mailmsg.Fields.Add(\"http://www.zxbc.cn/"http://schemas.microsoft.com/cdo/configuration/smtpauthenticate/"\", \"1\");//1 is to certify
            //the user id   
            mailmsg.Fields.Add( 
                        sequence_set,
                        IMAP_FetchItem_Flags.UID | IMAP_FetchItem_Flags.MessageFlags | IMAP_FetchItem_Flags.Size | IMAP_FetchItem_Flags.Envelope,
                        true, false
                        );
                //int count =0;
                foreach (IMAP_FetchItem fetchItem in fetchItems)
                {
                    IMAP_Envelope envelope = fetchItem.Envelope;
                    //hanldle it, means read and search and reply
                    try
                    {
                        HandleMail(envelope);
                        //count++;

}
                    catch (Exception ex)
                    {
                        Log(\"Sys\", ex.Message);
                    } [Page]
                }
                //delete it after hanlde
                clnt.DeleteMessages(sequence_set, false);
                //disconnect
                clnt.Disconnect();
                //MessageBox.Show(count.ToString() + \" of \" + fetchItems .Length+ \" Success\");
            }
            catch (Exception x)
            {
                Log(\"Sys\", x.Message);
                //MessageBox.Show(x.Message);
            }
 
。。
上边都是如何收邮件。
关于如何发送邮件是比较简单的。这里提供两种方式。
第一种方式是使用网上的smtp。这种方式必须要提供用户名和密码。这个适合于web应用，使用的smtp也是网上的，我一般使用163的smtp，基本没有问题。
第二种方式是使用本地的smtp。不需要提供密码，用户也可以是不存在的（垃圾邮件是不是就是这么产生的？），但是必要要提供smtp端口号。
第二种方法测试的时候有时候会报错“Mailbox unavailable. The server response was: 5.7.1 Unable to relay for xxx”，查过资料之后（在baidu上没找到，还是google信息多一点），才发现问题原来是IIS里SMTP服务的配置有问题。
这样修改可以解决：到开SMTP属性—>Access页面Reply Restrictions/ Reply-Only this Below选项，加上自己的ip：127.0.0.1（允许本机，使用loalhost，如果是允许其他机器，类似设置）
代码如下
public class EMail
    {
        static public string accountName;
        static public string password;
        static public string smtpServer;
        static public int smtpPort;
        /// <summary>
        /// need password,username, smtpserver
        /// </summary> [Page]
        /// <param name=\"to\"></param>
        /// <param name=\"subject\"></param>
        /// <param name=\"body\"></param>
        static public void SendMail(string sendTo, string subject, string body)
        {
            //.net smtp 
            System.Web.Mail.MailMessage mailmsg = new System.Web.Mail.MailMessage();
            mailmsg.To = sendTo;
            //mailmsg.Cc = cc;
            mailmsg.Subject = subject;
            mailmsg.Body = body;
            //sender here
            mailmsg.From = EMail.accountName; 
            // certify needed  
            mailmsg.Fields.Add(\"http://www.zxbc.cn/"http://schemas.microsoft.com/cdo/configuration/smtpauthenticate/"\", \"1\");//1 is to certify
            //the user id   
            mailmsg.Fields.Add(

"http://www.zxbc.cn/"http://schemas.microsoft.com/cdo/configuration/sendusername/"\",
                EMail.accountName);
             //the password
            mailmsg.Fields.Add(
                \"http://www.zxbc.cn/"http://schemas.microsoft.com/cdo/configuration/sendpassword/"\",
                 EMail.password);
            System.Web.Mail.SmtpMail.SmtpServer = EMail.smtpServer;
            System.Web.Mail.SmtpMail.Send(mailmsg); [Page]
        }

#region send mail2
        /// <summary>
        /// need username,smtp,smtp port
        /// </summary>
        /// <param name=\"sendTo\"></param>
        /// <param name=\"subject\"></param>
        /// <param name=\"body\"></param>
        static public void SendMail2(string sendTo, string subject, string body)
        {
            System.Net.Mail.MailMessage msg = new System.Net.Mail.MailMessage();
            msg.To.Add(sendTo);
            msg.From = new System.Net.Mail.MailAddress(accountName );
            msg.Subject = subject;
            msg.SubjectEncoding = System.Text.Encoding.UTF8;
            msg.Body = body;//
            msg.BodyEncoding = System.Text.Encoding.UTF8;
            msg.IsBodyHtml = false;
            //msg.Priority = MailPriority.High;//
            System.Net.Mail.SmtpClient client = new System.Net.Mail.SmtpClient();
            client.Host = smtpServer;
            client.Port = smtpPort;
            //client.Credentials = new System.Net.NetworkCredential(\"http://www.zxbc.cn/"mailto:user@xxx.com/"\", \"pass\"); 
            client.Send(msg);
        }
        #endregion
    }