SMTP client

• Download CSmtp.zip - 10.73 KB

Introduction

The CSmtp class allows to send emails from your program. The inspiration to write the CSmtp class was the article [1]. I have used the code of CFastSmtp and introduced the following changes:

• some bags have been removed (i.e. free memory),
• logining with authentication have been applied (AUTH LOGIN),
• sending attachments have been added,
• errors handling have been modified,
• new headlines from MIME specifications (i.e. X-Priority) have been added.

Typical scenarios while sending the email

After successfull connection to the SMTP server, our client starts the conversation between the remote SMTP server. Each line send by the client ought to be finished by "\r\n". If you want to know more details, check [2], [3], [4], [5], [6], [7], [8] and [9]. In [2] was described original SMTP protocol (1982),in [4] were discussed SMTP extensions for authentication and MIME specification was improved in [5]-[9]. Example 3 failed becouse no TLS procedures were implemented in the CSmtp class. If you want to add TLS see OpenSSL. I have introduced the following notation: S - is a remote server, C - is our client, xxx - means information censured.

Example 1 - Connecting to smtp.wp.pl and using incorrect login or password

S: 220 smtp.wp.pl ESMTP
C: EHLO: mydomain.com
S: 250-smtp.wp.pl
   250-PIPELINING
   250-AUTH=LOGIN PLAIN
   250-AUTH LOGIN PLAIN
   250-STARTTLS
   250-SIZE
   250-X-RCPTLIMIT 100
   250-8BITMIME
C: AUTH LOGIN
S: 334 VXNlcm5hbWU6
C: Kioq
S: 334 UGFzc3dvcmQ6
C: Kioq
S: 535 blad autoryzacji, niepoprawny login lub haslo / auth failure

Example 2 - Connecting to smtp.wp.pl and using correct login and password

S: 220 smtp.wp.pl ESMTP
C: EHLO: mydomain.com
S: 250-smtp.wp.pl
   250-PIPELINING
   250-AUTH=LOGIN PLAIN
   250-AUTH LOGIN PLAIN
   250-STARTTLS
   250-SIZE
   250-X-RCPTLIMIT 100
   250-8BITMIME
C: AUTH LOGIN
S: 334 VXNlcm5hbWU6
C: xxx
S: 334 UGFzc3dvcmQ6
C: xxx
S: 235 go ahead
C: MAIL FROM:<me@mydomain.com>
S: 250 ok
C: RCPR TO:<friend@domain.com>
S: 250 ok
C: DATA
S: 234 go ahead
C: Date: Sun, 24 Aug 2008 22:43:45
   From: JP<mail@domain.com>
   X-Mailer: The Bat! (v3.02) Professional
   Replay-to:mail@domain.com
   X-Priority: 3 (Normal)
   To:<friend@domain.com>
   Subject: The message
   MIME Version 1.0
   Content-Type: multipart/mixed; boundary="__MESSAGE__ID__54yg6f6h6y456345"
   
   --__MESSAGE__ID__54yg6f6h6y456345
   Content-type: text/plain; charset=US-ASCII
   Content-Transfer-Encoding: 7bit

   This is my message.

   --__MESSAGE__ID__54yg6f6h6y456345
   Content-Type: application/x-msdownload; name="test.exe"
   Content-Transfer-Encoding: base64
   Content-Disposition: attachment; filename="test.exe"
   
   TVqQAAMAAAAEAAAA//8AALgAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
   (...)
   SU5HWFhQQURESU5HUEFERElOR1hYUEFERElOR1BBRERJTkdYWFBBRERJTkdQQURESU5HWA==
   --__MESSAGE__ID__54yg6f6h6y456345
   Content-Type: application/x-msdownload; name="test2.jpg"
   Content-Transfer-Encoding: base64
   Content-Disposition: attachment; filename="test2.jpg"
   
   /9j/4Sv+RXhpZgAASUkqAAgAAAAJAA8BAgAGAAAAegAAABABAgAWAAAAgAAAABIBAwABAAAA
   (...)
   A6YxR5YJJ5zUu6ZW4+NjC24E4q5Dcox5I+lRI0iWAAV9aay+lTctoYTjrml+9irRmz//2Q==
   
   --__MESSAGE__ID__54yg6f6h6y456345--
   
   .
   
S: 250 ok xxx qp xxx
C: QUIT
S: 221 smtp.wp.pl   

Example 3 - Connecting to smtp.gmail.com

S: 220 mx.google.com ESMTP
   w28sm1561195uge.4
C: EHLO: mydomain.com
S: 250-mx.google.com at your service [xxx.xxx.xxx.xxx],
   250-SIZE 28311552
   250-8BITMIME
   250-STARTTLS
   250 ENHANCEDSTATUSCODES
C: AUTH LOGIN
S: 530 5.7.0 Must issue a STARTTLS command first. w28sm1561195uge.4

Example 4 - Connecting to smtp.bizmail.yahoo.com and using incorrect login or password

S: 220 smtp103.biz.mail.re2.yahoo.com ESMTP
C: EHLO: mydomain.com
S: 250-smtp103.biz.mail.re2.yahoo.com
   250-AUTH LOGIN PLAIN XYMCOOKIE
   250-PIPELINING
   250-8BITMIME
C: AUTH LOGIN
S: 334 VXNlcm5hbWU6
C: dG9t
S: 334 UGFzc3dvcmQ6
C: bmVyb24xMg==
S: 535 authorization failed (#5.7.0)

Implementation of the CSmtp class

1. Initialise winsock2 (function: WSAStartup)
2. Connect to the remote server (functions: gethostbyname, gethostbyaddr, socket, htons, getservbyname)
3. Introduce yourself - EHLO <SP> <domain> <CRLF>
4. Send AUTH LOGIN <CRLF> and another commands described in "Typical scenarios while sending the email" (functions: send, recv)
5. Finish conversation with QUIT <CRLF>
6. Free winsock2 resources (function: WSACleanup)

Usage

#include "CSmtp.h"
#include <conio.h>

int main()
{
    CSmtp mail;

    if(mail.GetLastError() != CSMTP_NO_ERROR)
    {
        printf("Unable to initialise winsock2.\n");
        return -1;
    }

    mail.SetLogin("***");
    mail.SetPassword("***");
    mail.SetSenderName("JP");
    mail.SetSenderMail("mail@domain.com");
    mail.SetReplyTo("mail@domain.com");
    mail.SetSubject("The message");
    mail.AddRecipient("friend@domain.com");
    mail.SetXPriority(XPRIORITY_NORMAL);
    mail.SetXMailer("The Bat! (v3.02) Professional");
    mail.SetMessageBody("This is my message.");
    mail.AddAttachment("c:\\test.exe");
    mail.AddAttachment("c:\\test2.jpg");

    if( !mail.ConnectServer("smtp.wp.pl",25) ) 
    {
        printf("Unable to connect to the server.\n");
        return -1;
    }
    
    if( mail.Send() )
        printf("The mail was send successfully.\n");
    else
        printf("Unable to send the mail.\n");

    mail.Disconnect();
    return 0;
}

Author's notices

1. If you will have problems to send the email use the Visual Studio's debuger and analyse the conversation between your SMTP server, perhaps your server needs differend kind of the authentication or doesn't need it at all.
2. You are not allowed to use CSmtp class to produce the spam.

Bibliography

1. CFastSmtp - Fast and easy SMTP class...
2. SIMPLE MAIL TRANSFER PROTOCOL RFC 821
3. STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES RFC 822
4. SMTP Service Extension for Authentication RFC 2554
5. MIME: Format of Internet Message Bodies RFC 2045
6. MIME: Media Types RFC 2046
7. MIME: Message Header Extensions for Non-ASCII Text RFC 2047
8. MIME: Registration Procedures RFC 2048
9. MIME: Conformance Criteria and Examples RFC 2049