What an MX record is
An MX (Mail Exchange) record is the DNS record that tells the rest of the internet where to deliver email for a domain. When someone sends a message to [email protected], their mail server looks up example.com's MX records to find which server should receive it. A domain can have several MX records, each with a priority number — lower numbers are tried first, so a priority-10 server is preferred over a priority-20 backup.
Looking up MX records tells you, at a glance, who handles a domain's email. Hostnames like aspmx.l.google.com mean Google Workspace; *.mail.protection.outlook.com means Microsoft 365; *.mx.cloudflare.net means Cloudflare Email Routing. It's the fastest way to identify a company's email provider from the outside.
Why check MX across multiple resolvers
If you've just changed your MX records — switching email providers, say — the change takes time to propagate, and different resolvers may still be serving the old records from cache. This tool queries several major public resolvers (Cloudflare, Google, Quad9, OpenDNS, AdGuard) at once and shows whether they agree. If they all return the same MX records, your mail routing is consistent and live. If they disagree, the change is still rolling out — mail could be going to either the old or new servers until it settles, which is exactly when email delivery problems appear.
Common reasons to do an MX lookup
Troubleshooting email delivery is the big one — if mail isn't arriving, wrong or missing MX records are a frequent culprit. Verifying a migration is another: after moving from one email provider to another, you check that the new MX records have propagated before decommissioning the old mailboxes. It's also used in competitive and security research to identify which email platform an organization runs, and in deliverability work alongside the SPF, DKIM, and DMARC records (which are TXT records — you can check those with the TXT record view).