Introduction

In a world where sensitive business information is regularly transmitted via email, it's imperative that your organization takes every step necessary to ensure the integrity and authenticity of your electronic communications. One such step is the implementation of DomainKeys Identified Mail (DKIM).

DKIM adds a digital signature to each outgoing email message. This signature verifies that the email originated from the specified domain and was not altered during transit - a powerful tool against email-based phishing and spoofing attacks. This tutorial will provide a practical, in-depth guide on how to set up DKIM for your business email servers.

1. Understand DKIM and its Importance

DKIM is an email authentication method that allows the receiver to check if the email was indeed sent by the domain it claims to be sent from and whether it was tampered with during transmission.

2. Generate a Pair of Keys

Tools needed: OpenSSL toolkit

On a Unix-like OS, you can use the OpenSSL toolkit to do this. Navigate to your chosen directory where you would like to store these keys. Run the following command:
openssl genrsa -out private.pem 1024
This will create a 1024-bit private RSA key and save it to a file named private.pem.

3. Extract the Public Key

Use this command to extract the public key from the private key:
openssl rsa -in private.pem -out public.pem -pubout -outform PEM

4. Create a TXT Record

The public key needs to be added to the DNS records of the domain used in the 'From:' field of the email. You'll need to create a TXT record for the selector (which can be any name you choose) and your public key.

The DNS record should be in this format:
v=DKIM1; k=rsa; p=MIGfMA0...the rest of your public key

5. Configure Your Email Server

You’ll then need to configure your outgoing email server to cryptographically sign outgoing emails using the private RSA key generated in step 2. The precise steps for this are dependent on your mail server software.

6. Test Your DKIM Configuration

Once you’ve configured DKIM, you should send a test email to ensure it’s working correctly. Tools such as DKIMValidator can help you validate your configuration.

7. Continuously Monitor Your DKIM Configuration

It's important to periodically check your DKIM configuration to ensure that it's still functioning as intended. Regular monitoring will ensure that any issues are quickly detected and resolved.