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.

If your IP address is dynamic, most SMTP servers reject your connection due to anti-spam policy. We always suggest that your send email by a SMTP server that has a static internet IP address. When you relay email by your SMTP server, because you do user authentication at first before you send email to your SMTP server, so your SMTP server doesn’t reject your connection even your IP address is dynamic. Finally your SMTP server sends email to remote SMTP server. Because your SMTP server has a static IP, the email won’t be rejected by remote SMTP server.
If you encountered a temporal SMTP error (4xx), you should retry to send email later. That means you have to write the code to handle retry. So if you have a static IP address, I suggest that you use EASendMail Component + EASendMail Service, EASendMail service can send email directly or send email with specified SMTP server in background and handle delivery retry automatically.

To learn more detail about EASendMail Serivce, please have a look at Work with EASendMail Service (Email Queuing).

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.