There are few things more frustrating for a business owner than realizing that important emails are not reaching their destination, or worse, that customers cannot email you. When you try to send a message and receive an immediate "Delivery Status Notification (Failure)" or "Undeliverable" bounce-back, panic often sets in.
While email delivery relies on a complex web of protocols and spam filters, the most common culprit for catastrophic, domain-wide email failure is surprisingly simple: misconfigured MX records.
In this guide, we will explain exactly what MX records are, how they control your email routing, and how you can use a free MX Record Lookup tool to troubleshoot and fix your bouncing emails.
What Are MX Records?
To understand why your emails are bouncing, you need to understand how the internet routes mail.
MX stands for Mail Exchange. It is a specific type of DNS (Domain Name System) record. Think of DNS as the internet's phonebook. When you type a website URL into your browser, DNS looks up the IP address for that website (using an A record).
When you send an email to hello@example.com, your email provider's server looks up the MX records for example.com. The MX records explicitly tell your server: "Hey, if you have mail for this domain, hand it over to these specific mail servers."
If the MX records are missing, pointing to the wrong place, or formatted incorrectly, the sending server throws its hands up in confusion and returns the email to you as undeliverable.
The Anatomy of an MX Record
An MX record contains two critical pieces of information:
- Mail Server (Exchange): The actual hostname of the server responsible for receiving the email. (e.g.,
aspmx.l.google.comif you use Google Workspace). - Priority: A number indicating preference. Lower numbers mean higher priority.
Most businesses have multiple MX records for redundancy. If the server with Priority 1 is down for maintenance, the sending server will automatically try to deliver the email to the server with Priority 5.
4 Reasons Why MX Records Cause Bounced Emails
If your emails are suddenly bouncing, one of these four MX record issues is almost certainly the cause.
1. You Recently Migrated Your Website or Domain
This is the number one cause of email outages. When you move your website to a new host (like moving from GoDaddy to Shopify or WPEngine), you often change your domain's nameservers.
When you change nameservers, your old DNS records (including your MX records) are left behind. Unless you manually copy your MX records to your new host's DNS settings, your domain suddenly has no instructions on where to send email.
2. You Switched Email Providers
If you recently upgraded from your web host's default email to a professional suite like Google Workspace or Microsoft 365, you must update your MX records to point to their specific servers. If you skipped this step, your email will still route to your old inbox—or bounce entirely if the old inbox was deleted.
3. Typographical Errors in the DNS Panel
DNS records are unforgiving. A single typo in the mail server hostname, or accidentally inputting the Priority number into the wrong field in your domain registrar's panel, will invalidate the record.
4. DNS Propagation Delays
If you did just update your MX records, you might still experience bounces for several hours. This is due to DNS propagation. Internet Service Providers cache DNS records based on their Time-To-Live (TTL) settings. It can take anywhere from 15 minutes to 48 hours for the world's servers to realize your MX records have changed.
How to Check Your MX Records Right Now
You do not need to log into your domain registrar to see your live MX records. You can check them publicly.
- Go to the free MX Record Lookup tool on FluxToolkit.
- Type in your domain name (e.g.,
yourbusiness.com). - Click Lookup MX.
Analyzing the Results
- Are there records listed? If the result says "No MX records found," you have found the problem. Your domain has no email routing instructions. Log into your domain registrar (like Namecheap or Cloudflare) and add them.
- Do the hostnames match your provider? If you use Microsoft 365, but the MX records point to
mail.bluehost.com, your email is routing to the wrong provider. - Are the priorities correct? Ensure that the primary server provided by your email host has the lowest priority number.
How to Fix It: Adding the Right Records
If you determine that your MX records are missing or incorrect, you need to log into your DNS provider (wherever you bought your domain, or wherever your nameservers point) and add the correct records provided by your email host.
For reference, here are the standard MX records for the two most popular providers:
Google Workspace (New Setup):
- Priority: 1
- Mail Server:
smtp.google.com
Microsoft 365:
- Priority: 0
- Mail Server:
yourdomain-com.mail.protection.outlook.com(Note: this is unique to your domain).
Once you save the new records in your DNS dashboard, use the MX Record Lookup tool again to verify that they are propagating correctly.
Conclusion
Bouncing emails are terrifying for business, but they are rarely a mystery. By understanding that MX records act as the internet's mail-routing instructions, you can quickly diagnose delivery failures. Before you spend hours on hold with customer support, run your domain through an MX lookup tool—the answer is usually hiding in plain sight.
Frequently Asked Questions (FAQ)
What is the difference between an A record and an MX record?
An A (Address) record maps a domain name (like website.com) to an IP address, allowing browsers to find your website. An MX (Mail Exchange) record specifically tells mail servers where to deliver emails addressed to that domain. They handle two completely different types of internet traffic.
Can I have MX records pointing to two different email providers?
Technically yes, but it is highly discouraged and will cause "split delivery" issues. If you have an MX record for Google and an MX record for Microsoft, sending servers will get confused. Some emails will end up in your Google inbox, and others will end up in Microsoft. You should only use MX records for a single active email provider.
Why do my MX records have numbers like 1, 5, and 10?
These are Priority numbers. They provide a failover system. A sending mail server will always attempt to deliver to the MX record with the lowest number first (e.g., Priority 1). If that server is offline, it will attempt the next lowest number (Priority 5).
How long does it take for MX record changes to take effect?
DNS changes are not instant. The time it takes for changes to propagate globally depends on the previous record's Time-To-Live (TTL) value. Typically, changes start taking effect within 15 to 30 minutes, but it can take up to 24 to 48 hours for all servers worldwide to recognize the new MX records.
My MX records are correct, but my emails are going to spam. Why?
MX records only control receiving email. If the emails you send are going to your recipients' spam folders, you have a sender authentication problem. You need to configure your SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC records to prove to other servers that you are a legitimate sender.
