Visual C++ - Sign Email - S/MIME

The following c++ example codes demonstrate how to sign email to S/MIME format with digital signature.

Email Digital Signature

Digital signature prevents email content is faked or changed in transport level. Encrypting email protects email content from exposure to inappropriate recipients. Both digital signature and email encrypting depend on digital certificate.

If you have an email digital signature certificate installed on your machine, you can find it in “Control Panel” -> “Internet Options” -> “Content” -> “Certificates” -> “Personal”.

email ceritificate

Then you can use your email certificate to sign the email by the following code. If you don’t have a certificate for your email address, you MUST get a digital certificate for personal email protection from third-party certificate authorities such as www.verisign.com.

If you need a free certificate for your email address, you can go to http://www.comodo.com/home/email-security/free-email-certificate.php to apply for one year free email certificate.

Installation

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.

Add Reference

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 project folder.

add reference in Visual C++

C++ - Sign Email - S/MIME - Example

The following example codes demonstrate signing email with digital signature - S/MIME. 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 "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("email from Visual C++ with digital signature(S/MIME)");

    // Set email body
    oSmtp->BodyText = _T("this is a test email sent from Visual C++ with digital signature");

    // 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");

    // If your SMTP server requires SSL connection, please add this line
    //oSmtp->SSL_init();

    // Add signer digital signature
    if( oSmtp->SignerCert->FindSubject(_T("test@emailarchitect.net"),
        CERT_SYSTEM_STORE_CURRENT_USER , _T("my")) == VARIANT_FALSE )
    {
        _tprintf(_T("Error with signer certificate; %s\r\n"),
            (const TCHAR*)oSmtp->SignerCert->GetLastError());
        return 0;
    }

    if( oSmtp->SignerCert->HasPrivateKey == VARIANT_FALSE )
    {
        _tprintf(_T("certificate does not have a private key, it can not sign email.\r\n" ));
        return 0;
    }

    _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;
}

Signature Algorithm

You can use SignatureHashAlgorithm property to set MD5, SHA1, SHA256, SHA384 or SHA512 signature algorithm. SHA256 is recommended.

32bit/x64 ActiveX DLL

Seperate builds of run-time dll for 32 and x64 platform

File Platform
Installation Path\EASendMailObj.dll 32 bit
Installation Path\x64\EASendMailObj.dll 64 bit

Distribution

  • 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

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