What Are MX Records and Why Should You Look Them Up?

MX records are DNS entries that tell the internet which mail servers accept email for a domain, and in what order. You look them up to confirm a domain is actually configured to receive mail and to diagnose why messages bounce or disappear. If email to your domain fails, an MX lookup is usually the first check.

What an MX record actually contains

An MX (Mail Exchange) record maps a domain to one or more mail server hostnames. Each record carries a priority number, and the sending server tries the lowest number first. If that server is unreachable, it moves to the next priority.

A typical set looks like this:

The priority value is relative, not absolute — only the ordering matters. A domain with a single MX record has no fallback, so if that server goes down, mail is delayed or bounced.

Why you should look them up

• Confirm mail is configured at all. A domain with no MX record cannot receive email, even if it has a website.
• Troubleshoot delivery failures. If senders report bounces, a wrong or missing MX record is a common cause.
• Verify a migration. After moving mail to a new provider, the MX records must point to the new servers.
• Check for stale or conflicting entries. Old records left behind can route mail to servers that no longer exist.

How to run an MX lookup on MxToolbox

MxToolbox provides a free MX Lookup tool at mxtoolbox.com. The page states the test lists MX records for a domain in priority order.

1. Enter the domain name you want to check.
2. Run the lookup. The tool queries the domain's authoritative name server directly, so recent MX changes should appear immediately rather than waiting for cached copies to expire.
3. Read the results as a priority-ordered list of mail servers.

From the results you can go further:

• Diagnostics connects to the mail server, verifies reverse DNS records, performs a simple Open Relay check, and measures response time.
• Blacklist check tests each MX record's IP address against 105 DNS-based blacklists (RBLs/DNSBLs).

Note that the site requires JavaScript to run, so the lookup will not work with scripting disabled.

What to look for in the results

• No records returned — the domain is not set up to receive mail. This is the most common reason a domain silently drops email.
• Records pointing to an unexpected provider — mail is being delivered somewhere you did not intend, often a leftover from a previous host.
• A single record with no backup — no redundancy if that server fails.
• Priority values that contradict your intended order — the lowest number wins, so a mislabeled backup can become the primary path.
• Server unreachable or failing diagnostics — the record exists but the server does not respond, which points to a hosting or firewall problem rather than a DNS one.

Where this fits in a broader check

MX records only cover inbound mail routing. They say nothing about SPF, DKIM, or DMARC, which govern whether your outgoing mail is trusted. If mail is being rejected as spam rather than failing to arrive, the MX lookup will look correct and the problem lies elsewhere. Use the MX lookup first when the question is "is this domain set up to receive mail, and where does it go?"