What is DKIM and How to Set It Up for Email Security

By Mithun • Published on June 30, 2025

Image credit: millionaire.email

DKIM (DomainKeys Identified Mail) is one of the most powerful tools for email authentication. It protects email senders and recipients from forged addresses and tampering during transit.

🔐 What is DKIM?

DKIM adds a digital signature to the email header. This signature is created using a private key and verified using a public key published in your DNS. When the recipient’s server receives the message, it verifies the DKIM signature to ensure the content wasn’t altered and is really from you.

🧬 Example DKIM Record

    default._domainkey.yourdomain.com IN TXT "v=DKIM1; k=rsa; p=MIGfMA0G...IDAQAB"
    

• default: selector name
• _domainkey: required suffix
• p=: your public key

⚙️ How to Set Up DKIM

1. Generate a DKIM key pair (private and public)
2. Add the public key to your DNS as a TXT record
3. Configure your mail server to sign outgoing emails with the private key
4. Test using DKIM Core Key Checker

✅ Benefits of DKIM

• Authenticates the email source
• Improves deliverability
• Works with SPF and DMARC for layered security

🚫 Common DKIM Pitfalls

• Misconfigured DNS record (wrong key format or selector)
• Too long TXT records (split them if needed)
• Using the same DKIM key for multiple domains

"DKIM is not just about security — it’s about trust in every email you send."