MX Records Explained by What Breaks Without Them
Missing, stale and half-dead MX records: the three ways email delivery breaks, and the order to check them in.
Most DNS records are invisible when they work. MX records are the exception people meet the hard way: set up a new domain, forget them, and discover a week later that every email sent to you has been bouncing into the void. This post explains MX records the practical way, by walking through exactly what breaks, in what order, when they are missing or wrong.
What an MX record does
MX stands for mail exchanger. When someone sends an email to [email protected], their mail server asks DNS a single question: which servers accept mail for this domain? The MX records are the answer, a short list of hostnames, each with a priority number. Senders try the lowest number first and work down the list if it does not answer. No MX records, no answer, and the sending server has nowhere to deliver. Nothing else in your DNS, not your website's records, not your SPF record, substitutes for them.
Breakage one: you receive nothing at all
This is the classic new-domain mistake, and it is total. Senders get a bounce, or occasionally a delayed failure after their server retries for days. From your side it looks like silence, which is why it is discovered late: nobody emails you to tell you your email is broken. Run your domain through the MX Checker and you should see your provider's servers listed, usually two or more, with sensible priorities. If the list is empty and you expect to receive mail, that is the whole problem.
Breakage two: mail arrives at the wrong place
MX records pointing at an old provider are worse than missing ones, because mail delivers successfully to a mailbox nobody opens. This happens after migrations: the website moved, the DNS was tidied, and the MX still names the previous host. It also happens the other way, a business moves to Google Workspace or Microsoft 365, updates everything except DNS, and wonders why the new inboxes stay empty while the old ones fill. The checker shows you which provider your records actually point at; we recognise the common ones and label them, so a mismatch with the service you pay for is obvious at a glance.
Breakage three: half your mail arrives
The subtle one. One MX target in the list is dead, a decommissioned server, a hostname that no longer resolves. Senders who try it first usually fall back to the next priority, so delivery mostly works, with random delays and the occasional bounce when a sender gives up early. In the checker, each of your MX hosts is resolved live; a host that fails to resolve is flagged. Delete dead entries. A short, correct list beats a long, hopeful one.
The order to check things in
Whenever email misbehaves on a domain, start with MX before anything clever: are there records, do they name the provider you actually use, does every host resolve? Only after that do the authentication records matter, and those are a separate check with the SPF, DKIM and DMARC Checker. Ten minutes with the MX records has ended more email mysteries than any other single step, because mail routing is simple, and it breaks in simple ways.