A Web based SMTP client program

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Introduction

This is a web based SMTP email program. This program can be used to send an email through a SMTP server. The user can specify a SMTP server's IP, sender's mail address, recipient's email address and mail content. When the user clicks on the "send mail" button , the mail is forwarded to the SMTP server which in turn forwards the mail to the recipient.

Details

This SMTP mail program is for .NET beta 2. I have written a SMTP email component in C# and compiled it into a dll. Then this dll is accessed through an aspx file which can be viewed in a browser.

Note: There is built in SMTP class already available in System.Web.Mail namespace . However it is worth taking a look at program below as it shows inner details of how to communicate with a SMTP server. Once you grasp this technique, you can modify it to communicate with any TCP socket server like FTP (for file access), HTTP (for web access), IRC (for chat) etc.

First I'll give the  source to the SMTP mail client.

/******************SMTPMail.cs ************ 
Name : SMTPMail.cs
Description : SMTP email client .
 Version : 1.0
 Author : Ravindra Sadaphule
  Email : ravi_sadaphule@hotmail.com
  Last Modified: 13th September , 2001
  To compile: csc /t:library /out:SMTPMail.dll SMTPMail.cs
  Note : save this file in c:/inetpub/wwwroot/bin directory
  */
namespace Ravindra
{
    /* SMTPClient is a class which inherits from TcpClient . Hence it can 
    access all protected and public membert of TcpClient
    */
public class SMTPClient : System.Net.Sockets.TcpClient
{
    public bool isConnected()
    {
        return Active ;
    }

    public void SendCommandToServer(string Command)
    {
        System.Net.Sockets.NetworkStream ns = this.GetStream() ;
        byte[] WriteBuffer ;
        WriteBuffer = new byte[1024] ;
        System.Text.ASCIIEncoding en = new System.Text.ASCIIEncoding() ;
        WriteBuffer = en.GetBytes(Command) ;
        ns.Write(WriteBuffer,0,WriteBuffer.Length);
        return ; 
    }

    public string GetServerResponse()
    {

        int StreamSize ;
        string ReturnValue = "" ;
        byte[] ReadBuffer ;
        System.Net.Sockets.NetworkStream ns = this.GetStream() ;
        ReadBuffer = new byte[1024] ;
        StreamSize = ns.Read(ReadBuffer,0,ReadBuffer.Length);
        if (StreamSize==0)
        {
            return ReturnValue ;
        }
        else
        {
            System.Text.ASCIIEncoding en = new System.Text.ASCIIEncoding() ;
            ReturnValue = en.GetString(ReadBuffer) ;
            return ReturnValue;
        }
    }

    public bool DoesStringContainSMTPCode(System.String s,System.String SMTPCode)
    {
        return (s.IndexOf(SMTPCode,0,10)==-1)?false:true ;
    }

 }// end of class SMTPClient



public class SMTPMail
{
    private System.String _SMTPServerIP = "127.0.0.1" ;
    private System.String _errmsg = "" ;
    private System.String _ServerResponse = "" ;
    private System.String _Identity = "expowin2k" ;
    private System.String _MailFrom = "" ;
    private System.String _MailTo = "" ;
    private System.String _MailData = "" ;
    private System.String _Subject = "" ;

    public System.String Subject // This property contains Subject of email
    {
        set
        {
            _Subject = value ;
        }
    }

    public System.String Identity // This property contains Sender's Identity
    {
        set
        {
            _Identity = value ;
        }
    }

    public System.String MailFrom // This property contains sender's email address
    {
        set
        {
            _MailFrom = value ;
        }
    }

    public System.String MailTo // This property contains recepient's email address
    {
        set
        {
            _MailTo = value ;
        }
    }

    public System.String MailData // This property contains email message
    {
        set
        {
            _MailData = value ;
        }
    }

    public System.String SMTPServerIP // This property contains of SMTP server IP
    {
        get
        {
            return _SMTPServerIP ;
        }
        set
        {
            _SMTPServerIP = value ;
        }
    }

    public System.String ErrorMessage // This property contais error message
    {
        get
        {
            return _errmsg ;
        }
    }

    public System.String ServerResponse // This property contains  server response
    {
        get
        {
            return _ServerResponse ;
        }
    }

    public void SendMail()
    {
        try
        {
            System.String ServerResponse ;
            SMTPClient tcp = new SMTPClient() ; 
            tcp.Connect(SMTPServerIP,25) ; // first connect to smtp server
            bool blnConnect = tcp.isConnected();

            // test for successful connection
            if (!blnConnect)
            {
                _errmsg = "Connetion Failed..." ;
                return; 
                                                        }

            //read response of the server 
            ServerResponse = tcp.GetServerResponse() ;
            if (tcp.DoesStringContainSMTPCode(ServerResponse,"220"))
            {
                _ServerResponse += ServerResponse ;
            }
            else
            {
                _errmsg = "connection failed" + ServerResponse ; 
                 return ;
            }
            System.String[] SendBuffer = new System.String[6] ;;
            System.String[] ResponseCode = {"220","250","251","354","221"}; 

            System.String StrTemp = "" ;
            StrTemp = System.String.Concat("HELO ",_Identity);
            StrTemp = System.String.Concat(StrTemp,"\r\n");
            SendBuffer[0] = StrTemp ;
            StrTemp = "" ;
            StrTemp = System.String.Concat("MAIL FROM: ",_MailFrom);
            StrTemp = System.String.Concat(StrTemp,"\r\n");
            SendBuffer[1] = StrTemp ;

            StrTemp = "" ;
            StrTemp = System.String.Concat("RCPT TO: ",_MailTo);
            StrTemp = System.String.Concat(StrTemp,"\r\n");
            SendBuffer[2] = StrTemp ;

            StrTemp = "" ;
            StrTemp = System.String.Concat("DATA","\r\n");
            SendBuffer[3] = StrTemp ;

            StrTemp = "" ;
            StrTemp = System.String.Concat("From: ",_MailFrom );
            StrTemp = System.String.Concat(StrTemp,"\r\n" );
            StrTemp = System.String.Concat(StrTemp,"To: " );
            StrTemp = System.String.Concat(StrTemp,_MailTo);
            StrTemp = System.String.Concat(StrTemp,"\r\n" );
            StrTemp = System.String.Concat(StrTemp,"Subject: " );
            StrTemp = System.String.Concat(StrTemp,_Subject);
            StrTemp = System.String.Concat(StrTemp,"\r\n" );

            StrTemp = System.String.Concat(StrTemp,_MailData);
            StrTemp = System.String.Concat(StrTemp,"\r\n.\r\n");
            SendBuffer[4] = StrTemp ;

            StrTemp = "" ;
            StrTemp = System.String.Concat(StrTemp,"QUIT\r\n");
            SendBuffer[5] = StrTemp ;

            int i = 0 ;
            /* for debugging
            _errmsg = "" ;
            for(i=0;i<5;i++)
            {
                _errmsg += SendBuffer[i] ;
                += "<br>" ;
            }
            return ;
            // end of debugging
            */

            while(i < SendBuffer.Length)
             {
                tcp.SendCommandToServer(SendBuffer[i]) ; 
                ServerResponse = tcp.GetServerResponse() ;
                for(int j=0;j<ResponseCode.Length;j++)
                {
                    if (tcp.DoesStringContainSMTPCode(ServerResponse,ResponseCode[j]))
                        {
                            _ServerResponse += ServerResponse;
                            _ServerResponse += "<br>";
                            break;
                        }
                    else
                    {
                        if(j==ResponseCode.Length-1)
                        {
                            _errmsg += ServerResponse ;
                                _errmsg += SendBuffer[i] ;
                            return ;
                        }
                    }
                }

                i++ ;
             } // end of while loop ;

        }// end of try block
        catch(System.Net.Sockets.SocketException se)
        {
            _errmsg += se.Message + " " + se.StackTrace;
        }
        catch(System.Exception e)
        {
            _errmsg += e.Message + " " + e.StackTrace;
        }
    } // end of SendMail method

 } // end of class client

 } // end of namespace Ravindra

 /*****************end of Modified SMTPMail.cs*********/

The program is big but quite simple . A class SMTPClient is derived from TcpClient . Hence all protected and public properties of TcpClient are available to SMTPClient class.

Now go directly to SendMail class. In this class I have added several private variables and corresponding properties like smtpserverIP, MailFrom, MailTo etc. These properties are set by the smtpMail.aspx program which is given below.

All these inputs are received from smtpMail.aspx file. In the SendMail() method of SMTPMail class an instance of SMTPClient class is created and connection to smtp server is attempted .The blnconnect flag indicates success/failure connection. If a connection fails, then an error message is generated and the program Terminates. 

On a successful connection (i.e. blnconnect is true) , the SMTP server's response is analyzed for success code "220". If SMTP responds with success code "220", then the action starts.

All SMTP commands are stored in array SendBuffer[] . All possible success codes from the SMTP server are stored in an array ResponseCode[]. So the commands from the array SendBuffer[] are sent to the SMTP server one by one and for each command the response from the SMTP server is analysed by comparing the SMTP server reply code with any of the possible success codes in the ResponseCode array. If the command executes successfully then only the next command is attempted. If any of commands is unsuccessful, then an error message is generated and the program terminates immediately.

Compile this smtpmail.cs file and put it into the c:/inetpub/wwwroot/bin directory.

Web based front end is given below. SMTPMail.aspx is put into c:\inetpub\wwwroot directory which is configured as the default website in IIS. This page can be viewed in browser by Typing url http://localhost/SMTPMAil.aspx.  The page shows some textboxes to capture input data like SMTP server ip ,sender's email , recepient;s email, subject, Mail Data etc. and a "Send Mail" button .

When user enters data into the textboxes and clicks on the "send Mail" button , a function btnSend_Click() is called. In this function  an instance of the SMTPMail class is created. Please remember that this SMTPMail class has been defined in the SMTPMAIL.cs file. Iin btnSend_Click() we capture inputs from user and set various properties of smail (an instance of SMTPMail) and call its sendmail() method.

If everything is OK , then a message "Mail Has been sent successfully" is displayed at the top of the page. If any error occurs, then an error message is displayed at the top.

<%@ Import NameSpace="Ravindra" %>
<script language="C#" runat="server">
void btnSend_Click(Object Sender,EventArgs e)
{
    if(Page.IsPostBack)
    {
        SMTPMail smail = new SMTPMail() ; ;
        smail.MailFrom = txtfrom.Text ;
        smail.MailTo = txtto.Text  ;
        smail.MailData = txtmessage.Text ;
        smail.Subject = txtSubject.Text ;
        smail.SMTPServerIP = txtSMTPServerIP.Text ;
        smail.SendMail();
        if (smail.ErrorMessage!="")
        {
            Response.Write("Error: " + smail.ErrorMessage) ;
        }
        else
        {
            /*
                for debugging only.
                    Response.Write(smail.ServerResponse + "Mail Sent successfully") ;
            */
            Response.Write("<br>Mail Sent successfully<br>") ; 
       }
    }
}

</script>
<html>
    <head>
        <title>SMTP E-Mail Example by Ravindra Sadaphule </title>
    </head>
    <body>
        <form name="frm1" runat="server" id="Form1">
            <table width="100%">
                <tr>
                    <td colspan="2" align="center">
                        <h3>
                            SMTP MAIL
                        </h3>
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                        SMTP SERVER IP:
                    </td>
                    <td width="70%" align="left" valign="middle">
                        <asp:textbox id="txtSMTPServerIP" runat="server" />
                        e.g. 127.0.0.1
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                        From:
                    </td>
                    <td width="70%" align="left" valign="middle">
                        <asp:textbox id="txtfrom" runat="server" />
                        e.g. ravi_sadaphule@hotmail.com
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                        To:
                    </td>
                    <td width="70%" align="left" valign="middle">
                        <asp:textbox id="txtto" runat="server" />
                        e.g. tarunt@bharat.com
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                        Sub:
                    </td>
                    <td width="50%" align="left" valign="middle">
                        <asp:textbox id="txtSubject" runat="server" />
                        e.g. Marriage Proposal
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                        Message:
                    </td>
                    <td width="70%" align="left" valign="middle">
                        <asp:textbox id="txtmessage" textmode="MultiLine" rows="5" runat="server" />
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                         
                    </td>
                    <td width="70%" align="left" valign="middle">
                        <asp:button text="Send Mail" id="btnSend" onclick="btnSend_Click" runat="server" />
                    </td>
                </tr>
                <tr>
                    <td width="30%" align="center" valign="middle">
                         
                    </td>
                    <td width="70%" align="left" valign="middle">
                        Developer:  <a href="mailto:ravi_sadaphule@hotmail.com">Ravindra Sadaphule</a>
                    </td>
                </tr>
            </table>
        </form>
    </body>
</html>