DKIM

DKIM (DomainKeys Identified Mail) is an email authentication protocol that adds a digital signature to outgoing emails. This signature is generated using a private key held by the sender's mail server and can be verified by the recipient's server using a public key published in the sender's DNS records. DKIM ensures that the email content has not been tampered with during transit, providing an additional layer of trust.

For B2B outreach teams, DKIM is an essential component of email authentication. While SPF verifies that the sending server is authorized, DKIM goes further by confirming message integrity. This dual verification gives receiving mail servers greater confidence that your emails are legitimate, which directly improves inbox placement rates.

Setting up DKIM involves generating a key pair, publishing the public key as a DNS TXT record, and configuring your mail server to sign outgoing messages with the private key. Most modern email service providers handle this configuration automatically, but it is important to verify that DKIM is active and functioning correctly, especially when using multiple sending services.

Key Points

• Uses public-key cryptography to sign and verify email messages
• Confirms that email content has not been modified during transit
• Works alongside SPF and DMARC for comprehensive email authentication

How It Works

When you send an email, your mail server creates a hash of the message content and encrypts it with your private key, attaching it as a DKIM signature header. The receiving server retrieves your public key from DNS, decrypts the hash, and compares it to its own hash of the received message. If they match, the email passes DKIM verification.

Best Practices

• Ensure DKIM is enabled for all sending domains and services you use
• Use a key length of at least 1024 bits, with 2048 bits recommended
• Periodically rotate your DKIM keys to maintain security