What happens if your MX record is missing?
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Imagine someone tries to email you and their mail server has no idea where to deliver it. That's exactly what happens when your MX record is missing. The sending server does a DNS lookup for your domain's mail exchanger and gets nothing back.
Here's what typically follows. Most modern mail servers will return a bounce with a message like "no MX record found" or "mail exchanger not available." The email never reaches you, and the sender gets a delivery failure notification. Some older sending software will fall back to your domain's A record (this is technically permitted by RFC 5321), but don't count on it. The majority of senders won't bother, and even when they do, your SPF record probably doesn't authorize that delivery path anyway, which means authentication failures on top of everything else.
The painful part is discovery. You won't get an alert that your MX record disappeared. You'll find out when a colleague mentions they never got your reply, or when a contact forwards you a bounce they received. That delay can stretch hours or even days depending on how urgently people are trying to reach you.
How to check if your MX record is missing
Run a quick DNS query in your terminal:
dig MX yourdomain.comSo if the answer section comes back empty, you've found your problem. You can also use an online DNS lookup tool if you'd rather not use the command line.
How to fix it
Log into your DNS provider (wherever you manage your domain's DNS records) and add an MX record pointing to your mail server. If you're using Google Workspace, that means adding Google's MX entries. If you're on Microsoft 365, you'll add Microsoft's. Your email host's documentation will give you the exact values and priority numbers to use.
How long until mail flows again
DNS changes propagate based on the TTL (time to live) value set on your records. Most providers default to somewhere between 5 minutes and an hour. Once the correct MX record is visible across DNS resolvers, senders can find your mail server again and delivery resumes. Emails that bounced while the record was missing are gone, though. Senders will need to resend those manually.
So if you're not sure whether your MX record is set up correctly right now, our free Email Header Analyzer can help you spot auth and routing issues. Or if things are broken and you need a second pair of eyes, our SOS hotline is free and we actually pick up.
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