DKIM Explained: How Cryptographic Signing Protects Your Emails
DKIM (DomainKeys Identified Mail) is the second layer of email authentication. It uses cryptographic signing to prove your emails are legitimate and unaltered.
DKIM (DomainKeys Identified Mail) is the second layer of email authentication. It uses cryptographic signing to prove your emails are legitimate and unaltered.
What DKIM does
When you send an email, your email server attaches a digital signature to the email header. This signature is created using a private key that only your server knows. The receiving server looks up the corresponding public key in your domain's DNS and uses it to verify the signature. If the signature validates, it proves two things: the email was genuinely sent from your domain (authenticity), and the email content was not changed in transit (integrity).
Why DKIM matters for cold email
DKIM is a trust signal. Emails with valid DKIM signatures are more likely to reach the inbox because the receiving server has cryptographic proof of their legitimacy. Without DKIM, your emails lack this proof, and providers treat them with more suspicion. DKIM is also required for DMARC alignment. Without DKIM, your DMARC policy cannot be fully enforced.
How to set up DKIM
For Google Workspace: Go to Admin Console > Apps > Google Workspace > Gmail > Authenticate Email. Generate a DKIM key. Copy the generated DNS record and add it as a TXT record to your domain's DNS. Return to the Admin Console and click "Start Authentication." For Microsoft 365: Go to Microsoft 365 Defender > Email & Collaboration > Policies > Email Authentication Settings > DKIM. Select your domain, and Microsoft will provide CNAME records to add to your DNS. After DNS propagation, enable DKIM signing. Verification: DKIM configuration can be verified as part of your overall DNS check using the DNS Checker at Warm Inboxes. You can also verify by sending a test email and checking the email headers for "dkim=pass."
Common DKIM mistakes
Forgetting to click "Start Authentication" after adding the DNS record (Google Workspace). Not waiting for DNS propagation before enabling DKIM. Using a 1024-bit key instead of a 2048-bit key (2048-bit is more secure and recommended).
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