MX Lookup

Query Mail Exchange (MX) DNS records for any domain — see mail servers and their priority

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Frequently Asked Questions

An MX (Mail Exchange) record is a DNS record that specifies which mail servers are responsible for receiving email for a domain. When someone sends an email to user@example.com, the sending mail server performs an MX lookup for example.com to find out where to deliver the message.

Priority (also called preference) is a number that determines which mail server should be tried first. A lower number means higher priority. For example, a server with priority 10 is tried before one with priority 20. If the primary server is unreachable, email is retried on the next-priority server. This provides redundancy.

If a domain has no MX records, it cannot receive email. This is common for domains used only for websites, API services, or subdomains. Some domains fall back to their A record for mail delivery (implicit MX), but this is not reliable or recommended. You should always set explicit MX records if you need to receive email.

The MX hostname usually reveals the provider: google.com in the hostname means Google Workspace (Gmail), outlook.com or protection.outlook.com means Microsoft 365 / Exchange Online, mimecast.com means Mimecast, pphosted.com means Proofpoint. Self-hosted mail servers often use the domain itself as the MX record.

MX priority (also called preference) is a number where lower = higher priority. When email is delivered, the sending server tries the mail server with the lowest priority number first. If that server is unavailable, it falls back to the next lowest number. For example, if a domain has MX records with priorities 10 and 20, the priority-10 server receives all mail; the priority-20 server only receives mail when priority-10 is unreachable. Google Workspace uses priority 1 for aspmx.l.google.com and higher numbers (5, 10) for backups.

Multiple MX records provide redundancy and failover. If the primary mail server (lowest priority number) is down for maintenance or experiences an outage, sending servers will automatically try the secondary MX records. This ensures email delivery continues even during server downtime. Major email providers like Google Workspace and Microsoft 365 configure 5+ MX records across different IP ranges and data centers to guarantee near-zero downtime for email delivery.

An MX record explicitly designates a hostname as a mail server for the domain — it points to a mail server's hostname, which then resolves via its A record to an IP. An A record simply maps a domain/subdomain to an IP address with no special email meaning. If a domain has no MX records, some legacy mail servers will attempt delivery to the IP in the domain's A record (implicit MX), but this is unreliable and not recommended. Always configure explicit MX records for any domain that needs to receive email.

After verifying your MX records are correct, test full email deliverability by: (1) sending a test email to a Gmail or Outlook address and checking if it lands in inbox or spam; (2) using mail-tester.com which assigns a deliverability score and reports SPF, DKIM, DMARC, blacklist, and content issues; (3) checking our SPF Lookup, DKIM Checker, and DMARC Lookup tools to verify your authentication stack; (4) using the Blacklist Checker to confirm your sending IP isn't listed.

Google Workspace domains (including gmail.com) use five MX records all pointing to Google's mail infrastructure, all with subdomain patterns of *.l.google.com. The primary record is aspmx.l.google.com (priority 1), followed by alt1.aspmx.l.google.com and alt2.aspmx.l.google.com (priority 5), then alt3.aspmx.l.google.com and alt4.aspmx.l.google.com (priority 10). If you're setting up Google Workspace for your own domain, your MX records should point to these same hostnames.

MX records control where inbound email is delivered — they list the servers authorised to receive mail for your domain. SPF (Sender Policy Framework) controls outbound email authentication — it specifies which servers are authorised to send email on behalf of your domain, published as a TXT record (e.g. v=spf1 include:_spf.google.com ~all). The mx mechanism in SPF (v=spf1 mx ~all) tells receivers that the servers listed in your MX records are also authorised to send mail — useful when your mail servers handle both sending and receiving.

About This MX Lookup

This free MX Lookup tool queries DNS Mail Exchange records in real time for any domain. It returns all mail exchange servers sorted by priority (lowest number = highest priority) and resolves each server's hostname to its IP address for quick verification of your email routing configuration.

When to use this tool

  • Verify that email is correctly configured for a domain
  • Identify which email provider or hosting service a domain uses
  • Troubleshoot email delivery issues by checking MX priority order
  • Check MX record propagation after a DNS change or migration

MX Record Fields

FieldDescription
PriorityPreference value — lower number = higher priority server
Mail ServerFully qualified domain name (FQDN) of the mail server
IP AddressResolved IP address of the mail server hostname
TTLTime to live — how long the record is cached (seconds)

Standards & References

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