Email remains one of the most important communication tools for businesses, but it is also one of the most common attack vectors for cybercriminals. If you're researching email authentication, you've likely come across three acronyms: SPF, DKIM, and DMARC.
Many business owners ask the same question:
"Do I really need all three?"
The short answer is yes.
Each protocol serves a different purpose, and relying on only one or two leaves security gaps that attackers can exploit. Here's how they work together and why a complete email authentication strategy matters.
SPF verifies which mail servers are authorized to send email for your domain.
When an email is received, the recipient's mail server checks the sending server's IP address against your SPF record published in DNS.
If the server is listed, SPF passes.
If it isn't, SPF fails.
SPF does not:
When someone forwards your email, the forwarding server usually isn't included in your SPF record, causing SPF to fail.
DKIM verifies that an email has not been altered after it was sent.
A cryptographic signature is attached to every outgoing message. Receiving servers validate that signature using a public key stored in your DNS.
If the signature matches, the message is authentic and hasn't been modified during transit.
DKIM does not:
DMARC builds on SPF and DKIM by providing policy enforcement and reporting.
Rather than simply checking authentication, DMARC answers two important questions:
DMARC can instruct providers to:
It also provides detailed reports showing who is sending email using your domain.
Your marketing platform is authorized in SPF, so newsletters send successfully.
Later, a customer forwards your email to a coworker.
The forwarding server isn't authorized in SPF.
Result:
Meanwhile, spoofed emails also have a chance of reaching inboxes because no policy exists telling providers to reject them.
Your messages are digitally signed.
Forwarded emails continue to validate correctly because the DKIM signature travels with the message.
However:
Legitimate email authenticates successfully.
An attacker spoofs your domain.
Results:
Every receiving provider makes its own decision.
Some reject.
Some send to spam.
Some may still deliver to the inbox.
You lose consistency and visibility.
Direct email works well.
Forwarded email becomes a problem.
Since forwarding causes SPF to fail and there is no DKIM signature to fall back on, DMARC enforces your policy.
If your policy is set to reject, legitimate forwarded email may never reach its destination.
Signed email works correctly.
Forwarding works.
However, there is no published list of authorized sending servers.
This creates challenges when:
Unsigned mail simply fails DMARC.
Everything works together exactly as designed.
Legitimate email:
Forwarded email:
Spoofed email:
You also receive DMARC reports showing attempted abuse and authentication trends.
This is the strongest and most reliable email authentication configuration.
One of the biggest misconceptions is believing SPF alone prevents spoofing.
It doesn't.
SPF authenticates the Return-Path (envelope sender)—not necessarily the email address your recipient actually sees.
An attacker could:
Without DMARC, that email can still appear legitimate.
DMARC solves this by requiring alignment.
The authenticated SPF or DKIM domain must match the visible From address.
If they don't align, DMARC treats the message as a failure and enforces your policy.
This closes one of the biggest loopholes in email authentication.
SPF requires the most ongoing attention.
You'll need to update your record whenever you:
Organizations with many cloud applications also need to stay under SPF's 10 DNS lookup limit.
DKIM is generally stable after deployment.
Occasionally you'll need to:
Many modern email platforms automate much of this process.
DMARC policies usually change very little after enforcement.
The important ongoing task is reviewing DMARC reports.
These reports help identify:
One of the most common issues we see at LI Tech Advisors is organizations that publish a DMARC record, enable enforcement, and then never review the reports again. Problems build quietly until legitimate email suddenly stops delivering—or attackers begin abusing overlooked services.
SPF, DKIM, and DMARC were never designed to compete with one another.
They were designed to work together.
Removing any one of these protocols creates gaps that can impact email deliverability, business communications, and protection against spoofing attacks.
For organizations that rely on email every day, implementing all three is no longer considered optional—it's the modern baseline for email security.
Not sure whether your domain is fully protected?
LI Tech Advisors helps businesses throughout Long Island implement, monitor, and maintain SPF, DKIM, and DMARC to improve email security and protect against domain spoofing.
Anthony has been in the MSP business since before the acronym existed. Managed IT once started as break-fix solutions and some light phone support.
Since then, he has seen the industry flourish into a landscape of platforms, cloud servers, software tools and AI . Tailoring network configurations and software stacks to the specific needs of each business.
In his current role, he focuses on proactive planning, ensuring clients can avoid potential issues altogether. This involves meticulous planning for enhanced business continuity, allowing swift resolution of any unforeseen challenges. What initially began as addressing "fires" through break-fix solutions has evolved into a proactive approach, ensuring that such issues are prevented from arising in the first place.
