Send email without SMTP server(DNS lookup)


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 resouce, the performance of "Send email Directly" is lower than sending email with specified SMTP server. Moreover, nowaday 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 learn more, please refer to the code in Samples.

Remarks

In our solid experience, we don't suggest that you send email directly.

Suggestions

Since there are some limitation with DNS lookup, to make your application can work fine in different environment, we have the following suggestions.

1. Providing options in your application that user can choose to send email with dns lookup or specified SMTP server.

2. Your application should retry to send email with a backup server if sending email failed with DNS lookup.

Example

' 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

Private Sub btnSendMail_Click() 

    Dim oSmtp As New EASendMailObjLib.Mail 
    oSmtp.LicenseCode = "TryIt" 

    ' Set your sender email address
    oSmtp.FromAddr = "test@emailarchitect.net" 

    ' Add recipient email address
    oSmtp.AddRecipientEx "support@emailarchitect.net", 0 

    ' Set email subject
    oSmtp.Subject = "simple email from VB 6.0 project" 

    ' Set email body
    oSmtp.BodyText = "this is a test email sent from VB 6.0 project, do not reply" 

    ' Do not set SMTP server address
    oSmtp.ServerAddr = "" 

    MsgBox "start to send email ..." 

    If oSmtp.SendMail() = 0 Then 
        MsgBox "email was sent successfully!" 
    Else 
        MsgBox "failed to send email with the following error:" & oSmtp.GetLastErrDescription() 
    End If 

End Sub 


// 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( __uuidof(EASendMailObjLib::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; 
} 

// 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

Unit Unit1; 

Interface 

Uses 
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, 
  Dialogs, StdCtrls, EASendMailObjLib_TLB; // add EASendMail Unit 

Type 
  TForm1 = Class(TForm) 
    Button1: TButton; 
    Procedure Button1Click(Sender: TObject); 
  private 
    { Private declarations } 
  public 
    { Public declarations } 
  End; 

Var 
  Form1: TForm1; 

Implementation 

{$R *.dfm} 

Procedure TForm1.Button1Click(Sender: TObject); 
Var 
  oSmtp : TMail; 
Begin 
  oSmtp := TMail.Create(Application); 
  oSmtp.LicenseCode := 'TryIt'; 

  // Set your sender email address
  oSmtp.FromAddr := 'test@emailarchitect.net'; 

  // Add recipient email address
  oSmtp.AddRecipientEx( 'support@emailarchitect.net', 0); 

  // Set email subject
  oSmtp.Subject := 'simple email from Delphi project'; 

  // Set email body
  oSmtp.BodyText := 'this is a test email sent from Delphi project, do not reply'; 

  // Do not set SMTP server address
  oSmtp.ServerAddr := ''; 

  ShowMessage( 'start to send email ...' ); 

  If oSmtp.SendMail() = 0 Then 
    ShowMessage( 'email was sent successfully!' ) 
  Else 
    ShowMessage( 'failed to send email with the following error: ' 
    + oSmtp.GetLastErrDescription()); 

End; 

End.

See Also

Using EASendMail ActiveX Object
Registration-free COM with Manifest File
User Authentication and SSL Connection
From, ReplyTo, Sender and Return-Path
Digital Signature and Email Encryption - S/MIME
DomainKeys Signature and DKIM Signature
Work with EASendMail Service(Mail Queuing)
Programming with Asynchronous Mode
Programming with FastSender
Mail vs. FastSender
Bulk Email Sender Guidelines
Process Bounced Email (Non-Delivery Report) and Email Tracking
Work with RTF and Word
EASendMail ActiveX Object References
EASendMail SMTP Component Samples