MX Record Lookup

About MX Record Lookup

The MX Record Lookup tool queries the DNS Mail Exchange (MX) records for any domain, listing all configured mail servers with their priority values and resolved IP addresses. MX records determine which servers receive email for a domain. Lower priority numbers indicate higher preference — mail is delivered to the lowest-priority server first, with higher-priority values as fallback. This tool is essential for diagnosing email delivery issues, verifying mail server configuration after migrating to a new email provider, confirming SPF record alignment, and identifying the email infrastructure of a domain (e.g. detecting whether a domain uses Google Workspace, Microsoft 365, or a self-hosted mail server).

Why use MX Record Lookup

• Shows all MX records with priority values and resolved IPs.
• Identifies the email provider (Google Workspace, M365, Proofpoint, etc.) from MX hostnames.
• Useful for diagnosing email delivery failures and verifying migrations.
• Results are real-time from public DNS resolvers.
• Shows all MX records with priority values and resolved A/AAAA addresses in one view.
• Identifies the email provider (Google Workspace, M365, Proofpoint, Mimecast) from MX hostnames automatically.

How to use MX Record Lookup

1. Enter a domain name in the input field.
2. Click Lookup to retrieve the MX records.
3. Review the list of mail servers with their priority values and IP addresses.
4. Click any hostname to open a full DNS lookup for that server.
5. Enter a domain name in the input field — no http:// or @ prefix needed.
6. Click Lookup to retrieve the MX records from the authoritative DNS resolver.
7. Review the list of mail servers with their priority values (lower = preferred).

When to use MX Record Lookup

• Verifying MX records after migrating to a new email provider.
• Diagnosing why email sent to a domain is bouncing or not delivering.
• Confirming which email infrastructure a domain uses.
• Checking MX record priority configuration for load balancing or failover.
• Verifying MX records after migrating to a new email provider (Workspace → M365 or vice versa).
• Confirming which email infrastructure a domain uses for vendor due diligence.

Examples

Tips

• Use widely separated priority values (10, 20, 30) rather than 10/11/12 — it makes failover ordering easier to reason about.
• Backup MX servers must spool and forward, not just accept and silently drop — most cloud providers handle this automatically.
• If you see only one MX record, your provider is single-server — fine for most domains but no automatic failover.
• MX records pointing to a CNAME are forbidden by RFC 2181 — always point MX to a hostname with an A/AAAA record.
• Combine MX changes with SPF and DMARC review — changing email providers without updating SPF causes rejection cascades.
• Monitor MX TTL — when migrating, lower TTL to 300s a day before cutover to minimize downtime risk.
• Some hosted email providers add multiple equal-priority MX records for round-robin load distribution — this is normal and intentional.

Frequently Asked Questions

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Glossary

MX record

Mail Exchange record — a DNS record type that specifies the mail server(s) responsible for receiving email for a domain, along with a priority value.

Priority

A 16-bit unsigned integer in each MX record. Lower values indicate higher preference. Mail is attempted at the lowest-priority server first.

Implicit MX

When a domain has no MX records, RFC 5321 specifies that mail should be delivered to the domain's A record. Generally not recommended in modern setups.

SMTP

Simple Mail Transfer Protocol (RFC 5321) — the standard for sending email between mail servers, typically on port 25 (server-to-server) or 587 (submission).

SPF

Sender Policy Framework — a TXT record that lists IPs authorized to send mail on behalf of a domain. Closely related to MX but distinct.

DKIM

DomainKeys Identified Mail — a TXT record containing a public key used to verify cryptographic signatures on outbound mail.

DMARC

Domain-based Message Authentication, Reporting and Conformance — a TXT record that specifies how to handle SPF/DKIM failures and where to send report aggregates.

Backup MX

A higher-priority-number MX server that accepts and spools mail when the primary server is unreachable, then forwards once the primary recovers.