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MX Records and Email Security: How SPF, DKIM, and DMARC Work Together

Learn how MX records relate to SPF, DKIM, and DMARC, why you need all of them, and common misconceptions about email security DNS records.

If you manage a domain that sends or receives email, you have probably seen references to MX records, SPF, DKIM, and DMARC. Each of these plays a different role in how email works, but it is easy to mix them up or assume one covers the others. They do not. Getting email right means understanding what each record does and why you need all of them working together.

This guide breaks down the relationship between MX records and email authentication records in plain language, so you can make sure your domain's email is both functional and protected.

MX Records Handle Inbound Email

MX records answer one question: where should email for your domain be delivered? When someone sends a message to you@yourdomain.com, their email server looks up the MX records for yourdomain.com to find out which mail server to deliver it to.

That is the full extent of what MX records do. They are a routing instruction. They say nothing about whether an email is legitimate, whether it has been tampered with, or what to do with suspicious messages. MX records are purely about getting inbound email to the right place.

You can check your MX records at any time with mxrecordchecker.com to confirm they point to the correct mail server.

SPF Records Handle Outbound Authorization

SPF (Sender Policy Framework) answers a different question: which servers are allowed to send email on behalf of your domain?

When you send an email from yourdomain.com, the receiving server checks your domain's SPF record to see if the server that sent the message is on the approved list. If it is not, the receiving server may flag the message as suspicious or reject it outright.

An SPF record is a TXT record in your DNS that lists authorized sending servers. For example, if you use Google Workspace to send email, your SPF record includes Google's mail servers. If you also use a transactional email service like SendGrid or Mailgun, those need to be in your SPF record too.

Here is what a typical SPF record looks like:

v=spf1 include:_spf.google.com include:sendgrid.net ~all

This says: Google's servers and SendGrid's servers are authorized to send email for my domain. Everything else should be treated with suspicion.

The key difference from MX records: SPF is about sending, MX is about receiving. They operate in opposite directions.

DKIM Records Handle Message Integrity

DKIM (DomainKeys Identified Mail) answers yet another question: was this email actually sent by the domain it claims to be from, and has it been modified in transit?

When your email server sends a message, it attaches a cryptographic signature to the email headers. The receiving server then looks up your DKIM public key (published as a DNS record) and uses it to verify the signature. If the signature checks out, the receiving server knows the message was genuinely sent by your domain and was not altered along the way.

DKIM records are TXT or CNAME records that your email provider generates for you. You do not write them yourself. Your provider gives you the values to add to your DNS.

Unlike SPF, which checks the sending server's identity, DKIM checks the message itself. Even if an email passes SPF, it could still fail DKIM if the content was modified by a relay server.

DMARC Records Tie Everything Together

DMARC (Domain-based Message Authentication, Reporting, and Conformance) answers the policy question: what should receiving servers do when an email fails SPF or DKIM checks?

Without DMARC, receiving servers make their own decisions about failed authentication. Some might deliver the email anyway, some might send it to spam, and others might reject it. DMARC lets you set a consistent policy.

A DMARC record looks like this:

v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@yourdomain.com

This tells receiving servers: if an email from my domain fails authentication, quarantine it (send it to spam). Also, send me aggregate reports about authentication results so I can monitor what is happening.

DMARC policies range from p=none (monitor only, take no action) to p=quarantine (send to spam) to p=reject (block the email entirely). Most businesses start with none to collect data, then gradually tighten the policy once they are confident their legitimate email is properly authenticated.

Common Misconceptions

"MX records protect against spoofing"

They do not. MX records only control where inbound email is delivered. They have no effect on whether someone can forge your domain in the From line of an email. That is the job of SPF, DKIM, and DMARC.

A domain with perfect MX records but no SPF, DKIM, or DMARC is wide open to spoofing. Anyone can send email that appears to come from your domain, and receiving servers have no way to verify it.

"SPF is enough on its own"

SPF is a good start, but it has limitations. It only checks the envelope sender (the Return-Path header), not the visible From address that users see. An attacker can set a different From address that appears legitimate while using their own server as the envelope sender.

DKIM adds message-level verification, and DMARC ties the visible From address to SPF and DKIM results. You need all three for meaningful protection.

"I only send email, so I do not need MX records"

Even if your domain is primarily used for sending (newsletters, transactional emails), you should still have MX records. Bounce notifications, reply emails, and delivery failure reports get sent back to your domain. Without MX records, those messages have nowhere to go, and some receiving servers may treat your outbound email with more suspicion if your domain cannot receive mail.

"Setting up one record fixes email deliverability"

Email deliverability depends on all these records working correctly together. Missing any one of them creates gaps. Your MX records might be perfect, but if your SPF record does not include all your sending services, emails from those services may land in spam or get rejected.

How They Work Together

Think of it as a complete system with different responsibilities:

MX records are your mailbox. They tell the postal service where to deliver letters addressed to you.

SPF records are your authorized sender list. They tell the world which post offices are allowed to send mail stamped with your return address.

DKIM records are your wax seal. They prove a letter genuinely came from you and was not opened or altered in transit.

DMARC records are your instructions to recipients. They say what to do if a letter arrives claiming to be from you but the seal is broken or it came from an unauthorized post office.

When all four are properly configured, receiving servers can confidently deliver your legitimate email to inboxes and reject or quarantine anything that does not pass the checks.

Checking Your Complete Email Setup

Start by verifying your MX records are correct at mxrecordchecker.com. This confirms your inbound email routing is working.

Then check your authentication records:

For ongoing monitoring across all of these records, deliverabilitychecker.com watches your email DNS configuration daily and alerts you if something breaks or changes unexpectedly.

What to Do Next

If you are starting from scratch, set up your records in this order:

  1. MX records first: get email flowing to the right server
  2. SPF record second: authorize your sending servers
  3. DKIM record third: enable message-level authentication (your email provider will give you the values)
  4. DMARC record last: start with p=none to monitor, then tighten over time

If you already have some of these records but not others, fill in the gaps. Every missing record is an opportunity for email problems, whether that is failed deliveries, messages landing in spam, or someone spoofing your domain.

Run your domain through mxrecordchecker.com right now to see where you stand on the MX side, then work through the authentication records from there.

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