Dries Buytaert

Securing my email with SPF, DKIM and DMARC

I use my own domain name for email. Unfortunately, I received a few emails about dries@buytaert.net being used for phishing attacks. It's not the first time, but hopefully it will be the last!

I finally added SPF, DKIM and DMARC protection to my domains:

  • Sender Policy Framework (SPF) restricts what servers can send emails using my domain name. To enable it, all I had to do is add a DNS record to my domain. The new DNS record specifies a list of authorized hostnames. Servers that receive an email from me, verify the hostname of the outgoing mail server against the approved list in my SPF DNS record.
  • Domain Keys Identified Mail (DKIM) uses public-key cryptography to make sure that my email isn't tampered with. My mail server keeps a private cryptographic key. When I send an email, my mail server uses the private key to embed a digital signature into my emails. In turn, your mail server/client validates the signature using the corresponding public key. The public key is made available through a DNS record associated with my domain name. (I use Google Workspace as my mail server, and it was easy to enable DKIM.)
  • Domain-based Message Authentication, Reporting and Conformance (DMARC) allows me specify how emails that fail the SPF or DKIM test should be handled. I can set policies to reject or quarantine spoofed emails.
A screenshot of my email headers showing that SPF, DKIM, and DMARC all pass
In Gmail, click 'Show Original' to see what email protection is in place.

Many data breaches and financial losses start with a phishing email. If you use your own domain name for email, take five minutes to check how well you're protected. You can use one of the many checkers. Here are some of the checkers I used:

Owning your own domain name can be a bit of work, but it's also super interesting. I enjoyed learning about SPF, DKIM and DMARC.

— Dries Buytaert

Dries Buytaert is an Open Source advocate and technology executive. More than 10,000 people are subscribed to his blog. Sign up to have new posts emailed to you or subscribe using RSS.

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