EASendMail SMTP Component > Developer Center > Example Codes > Visual C++ > Send Email using MX DNS lookup - Smart Host

Visual C++ - Send Email using MX DNS lookup - Smart Host

In general, we send email via specified SMTP server. How does the specified SMTP server know what address this email should be sent to? The answer is... it queries MX record of recipient's domain via DNS lookup. It then forwards this email to the SMTP server queried from DNS server. If recipient's server doesn't work fine, sender's SMTP server will send a failure-delivery report to the sender telling it failed to send out the email.

How does EASendMail SMTP component work with "Send email directly"? Firstly, it queries MX record for recipient address from DNS, then sends email to recipient's email server directly. In short, if no SMTP server is specified in the code, EASendMail will send email to recipient directly. Since querying DNS server consumes CPU time and networking resource, the performance of "Send email directly" is lower than sending email with specified SMTP server. Moreover, nowadays more and more SMTP servers block email sent from dynamic IP address, so we don't recommend you to use "Direct Send Email" except you have a static IP address or you encounter problem with your ISP SMTP server.

Every recipient may have different SMTP server, if there are multiple recipients in one message and you want to send email directly, you should send the email to the recipients one by one.

To implement this feature, you just need to put nothing to SMTP server address.

The following example codes demonstrate how to send email without specified SMTP server.

Installation

Before you can use the following sample codes, you should download the EASendMail Installer and install it on your machine at first.

Add Reference of EASendMail ActiveX Object to Visual C++ Project

To use EASendMail SMTP ActiveX Object in your C++ project, the first step is "Add header files of EASendMail to your project". Please go to "C:\Program Files\EASendMail\Samples_VC\simple.vcNative" or "C:\Program Files (x86)\EASendMail\Samples_VC\simple.vcNative" folder, find "easendmailobj.tlh" and "easendmailobj.tli", and then copy these files to your C++ project folder.

add reference in Visual C++

// The following example codes demonstrate sending email message using MX DNS lookup
// To get full sample projects, please download and install EASendMail on your machine.
// To run it correctly, please change SMTP server, user, password, sender, recipient value to yours

#include "stdafx.h"

#include "easendmailobj.tlh"
using namespace EASendMailObjLib;

int _tmain(int argc, _TCHAR* argv[])
{
    ::CoInitialize( NULL );

    IMailPtr oSmtp = NULL;
    oSmtp.CreateInstance( "EASendMailObj.Mail");
    oSmtp->LicenseCode = _T("TryIt");

    // Set your sender email address
    oSmtp->FromAddr = _T("test@emailarchitect.net");

    // Add recipient email address
    oSmtp->AddRecipientEx( _T("support@emailarchitect.net"), 0 );

    // Set email subject
    oSmtp->Subject = _T("simple email from Visual C++ project");

    // Set email body
    oSmtp->BodyText = _T("this is a test email sent from Visual C++ project, do not reply");

    // Do not set SMTP server address
    oSmtp->ServerAddr = _T("");

    _tprintf(_T("Start to send email ...\r\n" ));

    if( oSmtp->SendMail() == 0 )
    {
        _tprintf( _T("email was sent successfully!\r\n"));
    }
    else
    {
        _tprintf( _T("failed to send email with the following error: %s\r\n"),
            (const TCHAR*)oSmtp->GetLastErrDescription());
    }

    if( oSmtp != NULL )
        oSmtp.Release();

    return 0;
}

Comments

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Visual C++ - Send Email using MX DNS lookup - Smart Host

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