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Null MX Records: How to Stop a Domain From Receiving Email

Learn what a Null MX record is, how to configure one per RFC 7505, and when to use it for domains that should never receive email.

Not every domain needs to receive email. You might own a domain that is only used for a website, a domain you have parked to prevent someone else from registering it, or a domain that only sends transactional email and never needs an inbox. For these domains, a Null MX record is the correct way to tell the world that email delivery should not be attempted.

This guide explains what a Null MX record is, how it differs from simply having no MX records, and how to set one up.

What Is a Null MX Record?

A Null MX record is a special MX record defined in RFC 7505 that explicitly declares a domain does not accept email. It looks like this in DNS:

yourdomain.com.  IN  MX  0  .

The key parts are:

  • Priority: 0, the highest possible priority
  • Mail server: . (a single dot), this is the DNS root, which is not a valid mail server

When a sending server looks up your MX records and finds a Null MX, it knows immediately that the domain cannot receive email. Instead of trying to deliver the message and waiting for a timeout or bounce, it rejects the delivery attempt right away.

The single dot (.) is significant. In DNS, a dot by itself represents the root of the domain name system. It is not a real server. It is an explicit signal that no mail server exists for this domain.

How Null MX Differs From Having No MX Records

This is the most common point of confusion. Having no MX records at all is not the same as having a Null MX record, and the difference matters.

No MX Records At All

When a domain has zero MX records, sending servers do not simply give up. According to email standards (RFC 5321), they fall back to looking for an A record or AAAA record for the domain. If they find one (and most domains with websites do have an A record), they attempt to deliver email directly to that IP address on port 25.

This means a domain with no MX records but a web server can still receive email attempts. Those attempts will almost certainly fail (web servers are not mail servers), but the sending server does not know that in advance. It connects, tries to deliver, gets rejected, and then generates a bounce message back to the original sender.

This wastes resources on both sides and generates confusing bounce messages.

With a Null MX Record

A Null MX record changes this behavior. The sending server checks the MX records, sees the explicit Null MX, and immediately knows not to attempt delivery. No connection is made, no timeout occurs, and no bounce message is generated. The sending server returns a clean rejection to the original sender.

This is faster, cleaner, and unambiguous. It is the DNS equivalent of putting a sign on your door that says "no mailbox here" rather than having mail carriers walk up, try the door, find it locked, and leave a notice.

When to Use a Null MX Record

Parked Domains

If you own a domain purely to prevent someone else from registering it (a common typo of your main domain, a brand protection registration, or a domain you plan to use in the future), that domain should not accept email. A Null MX record makes this explicit.

Send-Only Domains

Some domains are used exclusively for sending email and never need to receive it. For example, you might use notifications.yourdomain.com to send transactional email through a service like SendGrid or Mailgun. If nobody should ever send email to that subdomain, a Null MX record is appropriate.

That said, be careful with this one. Even send-only domains sometimes need to receive bounce notifications and delivery failure reports. If your sending service handles bounces at their own domain (most do), a Null MX on your sending domain is fine. But if bounce handling requires email delivery to your domain, you need real MX records.

Website-Only Domains

If a domain only hosts a website and you have no email provider set up for it, adding a Null MX record prevents unwanted delivery attempts against your web server's IP address.

Domains Used for Non-Email Services

Some domains exist solely for API endpoints, CDN configurations, or other technical infrastructure. These domains have no business receiving email, and a Null MX record makes that clear.

How to Configure a Null MX Record

Setting up a Null MX record is straightforward. You add a single MX record at your DNS provider.

  1. Log into your DNS provider (your domain registrar or a service like Cloudflare)
  2. Navigate to DNS record management for your domain
  3. Add a new MX record with:
    • Host / Name: @ (for the root domain) or the subdomain name
    • Priority: 0
    • Mail Server / Value: . (just a single dot)
    • TTL: 3600 (or the default)
  4. Save the record

Make sure there are no other MX records for the same domain or subdomain. A Null MX record must be the only MX record present. If other MX records exist alongside it, sending servers may try those other records instead, defeating the purpose.

Provider-Specific Notes

Not all DNS providers handle the . value gracefully in their web interfaces. Some may reject it or add your domain name after it. Here is what to watch for:

  • Cloudflare: Enter . in the mail server field. Cloudflare supports this correctly.
  • GoDaddy: Enter . in the value field. May require you to enter it as a period without any additional text.
  • Namecheap: Enter . in the mail server field.
  • Route 53: Enter . in the value field. AWS supports Null MX natively.

If your DNS provider's web interface does not accept a single dot as a mail server value, contact their support. The Null MX standard has been around since 2015 (RFC 7505), and most modern DNS providers support it.

Verifying Your Null MX Record

After adding the record, check it at mxrecordchecker.com. Enter your domain and look at the results. You should see a single MX record with priority 0 pointing to . (the root).

If you see any other MX records alongside the Null MX, remove them. The Null MX must be the sole MX record for the domain.

If the tool shows no MX records at all, the record may not have propagated yet. Wait 15-30 minutes and check again. If it still does not appear, go back to your DNS provider and verify the record was saved.

Null MX and SPF Records

If your domain uses a Null MX record because it never receives email, you should also consider whether it sends email. If the domain does not send email either, add a restrictive SPF record to prevent spoofing:

v=spf1 -all

This tells receiving servers that no servers are authorized to send email from this domain. Combined with a Null MX record, you have clearly declared that the domain neither sends nor receives email.

If the domain does send email (the send-only scenario), your SPF record should authorize the sending service while the Null MX handles the receiving side:

v=spf1 include:sendgrid.net -all

You can check your SPF record at spfrecordcheck.com.

For complete protection on non-email domains, also add a DMARC record with a reject policy:

v=DMARC1; p=reject;

This tells receiving servers to outright reject any email claiming to come from your domain that fails authentication. Check your DMARC record at dmarcrecordchecker.com.

Null MX and Email Security

Domains without proper Null MX records (or without any MX records) are sometimes exploited by spammers. If a domain has no declared email policy, an attacker can send email that appears to come from that domain. Recipients have no way to verify whether the domain should be sending email at all.

By setting up a Null MX record, a restrictive SPF record, and a DMARC reject policy, you close this gap. You are making an explicit, verifiable declaration: this domain does not participate in email, period.

This is especially important for businesses that own multiple domains. Your primary domain might have full email infrastructure, but every secondary domain (brand variations, parked domains, old domains) should be locked down with Null MX and restrictive authentication records.

Common Mistakes

Adding a Null MX alongside other MX records. The Null MX must be the only MX record. Other MX records will be tried by sending servers regardless of the Null MX.

Confusing "no MX records" with Null MX. Removing all MX records does not achieve the same result. Sending servers will fall back to A record delivery, which creates failed delivery attempts and bounce messages.

Using Null MX on a domain that needs to receive bounces. If the domain sends email and the bounce path leads back to the same domain, you need real MX records to receive those bounces. Check with your sending service to confirm where bounces are handled.

Forgetting to check the result. After setting up a Null MX record, always verify at mxrecordchecker.com that it appears correctly. DNS interface quirks at some providers can silently modify or drop the . value.

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