Email is the backbone of business communication, but it’s also one of the most abused forms of messaging. Phishing, spoofing, and spam are costly, dangerous, and erode trust. The problem? Email was never designed with security in mind.
That’s where domain-level authentication comes in. Enter Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting and Conformance (DMARC) , the trio of protocols that help verify sender identity, protect your brand, and restore trust in the inbox. And when paired with visual trust signals like branded logos via Brand Indicators for Message Identification (BIMI) and Verified Mark Certificates (VMCs), you’re not just securing email, you’re elevating it.
- What is Sender Policy Framework?
- What is DomainKeys Identified Mail?
- What is Domain-based Message Authentication, Reporting and Conformance?
- How SPF, DKIM, and DMARC Work Together
- Why Implement These Protocols?
- Getting Started with Implementation
- Helpful Tools to Get You Started
What is Sender Policy Framework (SPF)?
SPF (Sender Policy Framework) is like a guest list for your domain. It tells receiving mail servers which IP addresses are allowed to send email on your behalf.
Think of SPF as your domain’s bouncer. Its job is to check whether the server sending an email in your name is invited. You do this by setting up an SPF record in your domain’s Domain Name System (DNS) , spelling out exactly which IP addresses are permitted to send on your behalf. For example, a typical record might look like: v=spf1 include:_spf.example.com ~all. This tells mail servers to trust email coming from specific sources while marking anything else as potentially suspicious.
Without SPF, your domain is vulnerable to impostors and bad actors who spoof your identity and use it to send phishing emails or spam. But once SPF is in place, it signals to inbox filters that you’re playing by the rules, and sets the stage for more advanced email authentication tools like DMARC and BIMI. SPF is your first line of defense and the foundation for supporting your reputation and building trust.
What is DomainKeys Identified Mail (DKIM)?
DKIM (DomainKeys Identified Mail) is like affixing a tamper-proof seal to every email your organization sends. Before your messages leave the server, DKIM has your mail system sign them using a private cryptographic key. Once they reach their destination, receiving servers check for that digital signature and use your public key, published in your domain’s DNS records, to validate its authenticity.
DKIM plays a vital role in ensuring that emails haven’t been altered or forged on their way from sender to recipient. In short, it tells your recipients’ systems: “Yes, this email came from us, and it hasn’t been messed with.”
And there's one more key reason DKIM matters: it's mandatory for VMCs. That means if you want your logo to show up in inboxes that support BIMI, DKIM isn’t optional, it’s foundational.
What is Domain-based Message Authentication, Reporting and Conformance (DMARC)?
DMARC (Domain-based Message Authentication, Reporting and Conformance) is essentially the policy architect behind email authentication. It connects the dots between SPF and DKIM, providing a unified voice that tells receiving mail servers how to handle messages that fail authentication checks.
The heart of DMARC lies in its policy options. When you set it to “None,” you’re in observation mode, watching and learning without taking any action. A “Quarantine” policy takes a cautious approach by sending questionable messages to the spam folder, while “Reject” enforces strict security by outright blocking unauthenticated emails from ever reaching the inbox. Each level gives you a different degree of control. Start with ‘none’ to monitor, ‘quarantine’ to flag, and ‘reject’ to fully enforce.
Why does all this matter? Because DMARC doesn’t just boost email security, it gives you valuable insight into how your domain is being used (or abused) across the internet. It empowers you to spot threats, protect your reputation, and steer the narrative around your brand. And if you’re looking to implement BIMI with VMCs, DMARC is the bridge that gets you there. Without it, your logo isn’t going anywhere near your recipients’ inboxes.
How do SPF, DKIM, and DMARC Work Together?
SPF, DKIM, and DMARC work as a coordinated team to bring order and integrity to your email ecosystem. SPF acts as your domain’s gatekeeper, verifying that the server sending your messages is authorized to do so. DKIM steps in to validate the integrity of the email’s content itself, applying a cryptographic signature to prove it hasn’t been tampered with along the way. Then DMARC ties the first two together, aligning authentication results and enforcing your domain’s policy on what to do with messages that don’t pass the checks, whether that means monitoring them, sending them to spam, or outright rejecting them.
When implemented together, they lay the technical foundation for visible brand authentication, making it possible to display your verified brand logo with standards like BIMI, supported through GlobalSign’s VMC. It’s layered protection with real-world impact, enhancing both trust and deliverability.
Why Should You Implement the SPF, DKIM and DMARC Protocols?
Email is often the first line of attack, with 91% of all cyber-attacks starting from a phishing email. Many cyber threats, like CEO impersonation or phony invoices, begin with something as deceptively simple as a spoofed message. The SPF, DKIM and DMARC protocols work together to block bad actors from pretending to be you. By verifying senders and authenticating messages, they shut down impersonation attempts before they ever reach your inbox. This leads to cleaner delivery, too: emails that pass authentication are more likely to land in the inbox instead of getting caught in spam filters.
Beyond technical protection, these protocols signal something more profound to your customers and partners, trust. When people know your messages are secure and verified, your domain earns credibility that’s hard to fake. And there’s a practical angle too: major email platforms like Google’s Gmail, Yahoo, and Microsoft’s Outlook and Hotmail now require SPF, DKIM, and DMARC for bulk senders . So, if you're sending campaigns or newsletters at scale, this is essential for compliance and reach.
Getting Started with Implementation
Here’s your quick-start checklist:
- Publish SPF records in DNS
- Set up DKIM keys and signatures
- Implement a DMARC policy (none to start) and monitor reports
Helpful Tools to Get You Started
Your domain is more than just a web address, it’s the digital handshake between your brand and the world. Protecting it means defending not only your reputation, but the trust you've built with customers, partners, and prospects. When properly implemented, these email authentication protocols verify that your messages are coming from legitimate sources, preserve content integrity, and empower receivers to enforce security policies. This doesn’t just reduce the risk of impersonation, it enhances your sender reputation, improves inbox placement, and signals professionalism every time your message lands.
And once those defenses are solid, you're poised to take that trust even further. With VMCs, you unlock visual branding inside inboxes, allowing your verified logo to appear alongside authenticated emails in supported platforms. It’s domain protection with a confidence boost, because in cybersecurity, visibility is trust.
