Managed C++/CLI - DomainKeys and DKIM Signature

The following Managed C++/CLI 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. To learn more detail about DomainKeys, please refer to http://antispam.yahoo.com/domainkeys

DKIM is a similar technology as Domainkeys. To learn more detail about DKIM, please refer to RFC4871.

Before you can add DomainKeys and DKIM signature to email, you need to generate the certificate and X-DK-File like this:

Download Certificate 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 Certificate” and save the downloaded pfx file to your local disk. This file contains your DomainKeys and DKIM key pair.

To sign the DomainKeys with EASendMail, we also need to create a text file with notepad and save it.

For example: We create a emailarchitectdomainkeys.txt and contains the following content:

dk_d: emailarchitect.net
dk_s: s1024
PFXPath: c:\my cert\emailarchitect.pfx
PFXPassword: mypassword
DKIM: yes
DomainKey: yes

// dk_d is the email sender domain,
// dk_s is the domain public key selector.
// PFXPath is the PFX file full path.
// PFXPassword is the PFX file password.

We also need to deploy the certificate Public Key to your domain DNS server. You can export the public key by the online tool:

https://www.emailarchitect.net/certs/getpublickey.aspx

Deploy Public Key

Once you get the public key, 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 =

        "t=y; k=rsa; p=MIGfMA0GCSqGS...hSinuQIDAQAB"

To learn more detail about Public Key deployment, please refer to http://antispam.yahoo.com/domainkeys

Installation

Before you can use the following codes, please download EASendMail SMTP Component and install it on your machine at first. Full sample proejcts are included in this installer.

Install from NuGet

You can also install the run-time assembly by NuGet. Run the following command in the NuGet Package Manager Console:

Install-Package EASendMail

Note

If you install it by NuGet, no sample projects are installed, only .NET assembly is installed.

Add Reference

To use EASendMail SMTP Component in your project, the first step is Add reference of EASendMail to your project. Please create or open your project with Visual Studio, then go to menu -> Project -> Add Reference -> .NET -> Browse..., and select EASendMail{version}.dll from your disk, click Open -> OK, the reference of EASendMail will be added to your project, and you can start to use it to send email in your project.

add reference in c#/vb.net/c++/cli/clr

.NET Assembly

Because EASendMail has separate builds for .Net Framework, please refer to the following table and choose the correct dll.

Separate builds of run-time assembly for .Net Framework 1.1, 2.0, 3.5, 4.0, 4.5 and .Net Compact Framework 2.0, 3.5.

File .NET Framework Version
EASendMail.dll Built with .NET Framework 1.1
It requires .NET Framework 1.1, 2.0, 3.5 or later version.
EASendMail20.dll Built with .NET Framework 2.0
It requires .NET Framework 2.0, 3.5 or later version.
EASendMail35.dll Built with .NET Framework 3.5
It requires .NET Framework 3.5 or later version.
EASendMaill40.dll Built with .NET Framework 4.0
It requires .NET Framework 4.0 or later version.
EASendMaill45.dll Built with .NET Framework 4.5
It requires .NET Framework 4.5 or later version.
EASendMailCF20.dll Built with .NET Compact Framework 2.0
It requires .NET Compact Framework 2.0, 3.5 or later version.
EASendMailCF35.dll Built with .NET Compact Framework 3.5
It requires .NET Compact Framework 3.5 or later version.

C++/CLI - DomainKeys and DKIM Signature - Example

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"

using namespace System;
using namespace EASendMail;

int main(array<System::String ^> ^args)
{
    SmtpMail ^oMail = gcnew SmtpMail("TryIt");
    SmtpClient ^oSmtp = gcnew SmtpClient();

    // Set sender email address, please change it to yours
    oMail->From = "test@emailarchitect.net";

    // Set recipient email address, please change it to yours
    oMail->To = "support@emailarchitect.net";

    // Set email subject
    oMail->Subject = "test email from Managed C++/CLI with DKIM";

    // Set email body
    oMail->TextBody = "this is a test email sent from Managed C++ project, do not reply";

    // Your SMTP server address
    SmtpServer ^oServer = gcnew SmtpServer("smtp.emailarchitect.net");

    // User and password for ESMTP authentication, if your server doesn't require
    // User authentication, please remove the following codes.
    oServer->User = "test@emailarchitect.net";
    oServer->Password = "testpassword";

    // If your SMTP server requires SSL connection, please add this line
    // oServer->ConnectType = SmtpConnectType::ConnectSSLAuto;

    // Add DomainKeys and DKIM configuration file
    // Then this email will be signed automatically
    oMail->Headers->ReplaceHeader("X-DK-File", "c:\\emailarchitectdomainkeys.txt");

    try
    {
        Console::WriteLine("start to send email from Managed C++...");
        oSmtp->SendMail(oServer, oMail);
        Console::WriteLine("email was sent successfully!");
    }
    catch (Exception ^ep)
    {
        Console::WriteLine("failed to send email with the following error:");
        Console::WriteLine(ep->Message);
    }

    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.

Appendix

Comments

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