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Relaymetry

MX lookup

Look up MX records for any domain. Instant, no signup, plain English.

Quick answer: MX records tell senders which servers accept inbound mail for your domain. Use this tool to confirm your MX records resolve, are ordered by priority, and point at hosts that can actually receive mail. A missing or broken MX record means inbound mail bounces; a stale entry from an old provider routes mail to a dead server.

What this checks

MX records are DNS records that route incoming mail for a domain to specific mail servers, ranked by priority. Relaymetry queries public DNS for the requested domain via the configured recursive resolver and returns each record's priority value, its target hostname, and whether that hostname resolves to one or more A or AAAA addresses. We do not test SMTP connectivity to the targets — that requires the TLS Check tool. Per RFC 5321 §5.1 and RFC 1035, MX targets must be hostnames with A or AAAA records, not CNAME aliases.

How to read the result

Lower priority numbers are tried first. A sending server attempts the MX with the lowest preference value, and falls back to higher numbers only if the primary host is unreachable or refuses the connection. Equal priorities distribute load across multiple hosts. Targets like aspmx.l.google.com indicate Google Workspace; <tenant>.mail.protection.outlook.com indicates Microsoft 365; vanity hosts like mail.<your-domain> indicate self-hosted or custom-branded routing through a provider. Multiple priority tiers (a primary at 10 and a backup at 20) are normal redundancy; a single record at priority 10 is also normal for many small operations. What matters is that every listed hostname resolves cleanly — the result page shows resolution status next to each target. Stale records from a previous mail provider commonly survive a migration; if the listed targets do not match the provider you currently use, the records need updating at your DNS host.

Common failures

No MX records returned: the domain has no published MX records, so receivers fall back to the A record per RFC 5321 §5.1 — a behavior most modern mailbox providers no longer rely on, so inbound mail typically bounces. Add MX records pointing at your mail provider's documented hostnames. MX target is a CNAME: RFC 2181 §10.3 forbids MX records from pointing at CNAME aliases. Many receivers reject such configurations outright. Replace the CNAME chain with a direct A or AAAA record at the MX target hostname. MX target is an IP literal: MX values must be hostnames, not IP addresses. Some DNS hosts will silently accept the entry but receivers will fail to resolve. Use a hostname with A or AAAA records. MX target hostname does not resolve: the target hostname has no A or AAAA records, so the receiver cannot connect. Verify the target spelling and that the target zone publishes its address records. Priority misordering: backup MX hosts at higher priority numbers will accept mail when the primary is down — but if the backup is misconfigured, it can absorb mail and silently drop it. Inventory every MX target. Stale records from old providers: inbound mail routes to a dead provider, and the rejection or silent drop produces no obvious bounce to the sender — making this failure mode hard to diagnose without an external check.

What this does not prove

MX records being valid does not guarantee mail will reach you. The receiving server must accept the SMTP connection, pass anti-abuse filtering, and actually deliver to the intended mailbox. We do not probe SMTP, do not authenticate that you control the mail servers, and do not verify the receiving infrastructure is healthy. Use the TLS Check tool to verify SMTP and STARTTLS posture, and run an end-to-end test by sending a real message from an external account if mail flow is suspect.

Common questions

Do I need an MX record?

Yes, if your domain is meant to receive email. Without an MX record, receivers fall back to the A record per RFC 5321 §5.1, but this fallback is rarely reliable — most mail will bounce. Domains used only for outbound sending technically do not require an MX record, but publishing one is recommended for clarity.

What does it mean when a domain has no MX records?

The domain is not configured to receive email. Inbound mail will likely bounce or never arrive. If you intended this domain to receive mail, add MX records using the hostnames documented by your mailbox provider (Google Workspace, Microsoft 365, Zoho, Fastmail, etc.).

Can an MX record point to a CNAME?

No. RFC 2181 §10.3 forbids MX targets from being CNAME aliases. Many receivers will reject mail to a domain whose MX points at a CNAME. The MX target must be a hostname with A or AAAA records directly.

Why do MX priorities matter?

Priorities tell senders which mail server to try first. The lowest preference value is tried first; higher values are fallbacks. Equal values distribute load. If your backup MX is misconfigured, it can silently swallow mail when the primary is down — so every MX target must be a working mail server.