The following example codes demonstrate how to add DomainKeys and DKIM signature to email and send it using SMTP server.
DKIM and DomainKeys
DomainKeys is a technology proposal that can bring black and white back to this decision process by giving email providers a mechanism for verifying both the domain of each email sender and the integrity of the messages sent. But DomainKey is deprecated by DKIM now,
DKIM is a similar technology as Domainkeys. To learn more detail about DKIM, please refer to RFC4871.
Before you can add DKIM signature to email, you need to generate the DKIM configuration file like this:
Download Json Configuration File for your DomainKeys/DKIM key pair
Please click here to go to this online tool at first. Then input your email sender domain in it and click “Download Configuration Json” and save the downloaded json file to your local disk. This file contains your DomainKeys and DKIM key pair.
Deploy Public Key
Once you get the json file, you can open it by notepad, and find the public key:
{
"CanonAlgorithm": 0,
"Domain": "emailarchitect.net",
"IsActive": true,
"IsSignPartOfMessage": false,
"RsaHashAlgorithm": 1,
"Selector": "s1024",
"PublicKey":"MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCydEgD9oTri865iNJqFVPJLEOW/uOHpjnnhMeGQQDodx/LqHlbs9iz3A95lXmFSlPgxCYNzGJPdqM7XXZnQCkaBO7DmKPJqdhgfOAECHOiT/5oXW9qMdQOymVdgy2iu2ZjKR2eXPnqYUHQycfQP82QigP3dLSi78xkruKlqlXvlQIDAQAB",
"PrivateKey":"-----BEGIN PRIVATE KEY-----\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\n-----END PRIVATE KEY-----\n",
"SignedHeaders": "sender:from:to:cc:date:subject:mime-version:content-type:message-id:in-reply-to",
"SignPartMessageLength": 0
}
You should set a TXT record in your domain DNS server. For example: your selector is s1024, your domain is emailarchitect.net, and then you should create a TXT record for s1024._domainkey.emailarchitect.net and set the following content in the record.
s1024._domainkey.emailarchitect.net text =
"v=DKIM1; k=rsa; p=MIGfMA0GCSqGS...hSinuQIDAQAB"
To learn more detail about Public Key deployment, please refer to https://www.emailarchitec.net/domainkeys/kb
Sections:
EASendMail is a SMTP component which supports all operations of SMTP/ESMTP protocols (RFC 821, RFC 822, RFC 2554). Before you can use the following example codes, you should download the EASendMail Installer and install it on your machine at first.
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\Include\tlh
or C:\Program Files (x86)\EASendMail\Include\tlh
folder,
find easendmailobj.tlh
and easendmailobj.tli
, and then copy these
files to your project folder.
The following example codes demonstrate sending email with DomainKeys and DKIM signature.
In order to run it correctly, please change SMTP server
, user
, password
, sender
, recipient
value to yours.
Note
To get full sample projects, please download and install EASendMail on your machine.
#include "stdafx.h"
#include <tchar.h>
#include <Windows.h>
#include "EASendMailObj.tlh"
using namespace EASendMailObjLib;
const int ConnectNormal = 0;
const int ConnectSSLAuto = 1;
const int ConnectSTARTTLS = 2;
const int ConnectDirectSSL = 3;
const int ConnectTryTLS = 4;
int _tmain(int argc, _TCHAR* argv[])
{
::CoInitialize(NULL);
IDkimConfigPtr dkimConfig = NULL;
dkimConfig.CreateInstance(__uuidof(EASendMailObjLib::DkimConfig));
// Load DomainKeys and DKIM configuration file
if (dkimConfig->LoadFromFile(_T("d:\\my folder\\emailarchitect.net.json")) != VARIANT_TRUE)
{
_tprintf(_T("failed to load dkim configuration file!"));
return 0;
}
IMailPtr oSmtp = NULL;
oSmtp.CreateInstance(__uuidof(EASendMailObjLib::Mail));
oSmtp->LicenseCode = _T("TryIt");
// Assign DkimConfig object to Smtp Mail
oSmtp->DkimSignerConfig = dkimConfig;
// 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++ with DKIM");
// Set email body
oSmtp->BodyText = _T("this is a test email sent from Visual C++ project, do not reply");
// Your SMTP server address
oSmtp->ServerAddr = _T("smtp.emailarchitect.net");
// User and password for ESMTP authentication, if your server doesn't
// require User authentication, please remove the following codes.
oSmtp->UserName = _T("test@emailarchitect.net");
oSmtp->Password = _T("testpassword");
// Most mordern SMTP servers require SSL/TLS connection now.
// ConnectTryTLS means if server supports SSL/TLS, SSL/TLS will be used automatically.
oSmtp->ConnectType = ConnectTryTLS;
// If your SMTP server uses 587 port
// oSmtp->ServerPort = 587;
// If your SMTP server requires SSL/TLS connection on 25/587/465 port
// oSmtp->ServerPort = 25; // 25 or 587 or 465
// oSmtp->ConnectType = ConnectSSLAuto;
_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());
}
return 0;
}
Remarks
If your SMTP server has implemented DKIM, you don’t have to sign DKIM in your codes, your email will be signed by your server automatically.
TLS is the successor of SSL, more and more SMTP servers require TLS 1.2
encryption now.
If your operating system is Windows XP/Vista/Windows 7/Windows 2003/2008/2008 R2/2012/2012 R2
, you need to
enable TLS 1.2 protocol in your operating system like this:
Enable TLS 1.2 on Windows XP/Vista/7/10/Windows 2008/2008 R2/2012
Seperate builds of run-time dll for 32 and x64 platform
File | Platform |
Installation Path\Lib\native\x86\EASendMailObj.dll | 32 bit |
Installation Path\Lib\native\x64\EASendMailObj.dll | 64 bit |
Standard EXE
For VB6, C++, Delphi or other standard exe application, you can distribute EASendMailObj.dll with your application to target machine without COM-registration and installer. To learn more detail, please have a look at Registration-free COM with Manifest File.
Script
For ASP, VBScript, VBA, MS SQL Stored Procedure, you need to install EASendMail on target machine by EASendMail installer, both 32bit/x64 DLL are installed and registered.
Appendix
Comments
If you have any comments or questions about above example codes, please click here to add your comments.